Add modular fib lookup framework.

This change introduces framework that allows to dynamically
 attach or detach longest prefix match (lpm) lookup algorithms
 to speed up datapath route tables lookups.

Framework takes care of handling initial synchronisation,
 route subscription, nhop/nhop groups reference and indexing,
 dataplane attachments and fib instance algorithm setup/teardown.
Framework features automatic algorithm selection, allowing for
 picking the best matching algorithm on-the-fly based on the
 amount of routes in the routing table.

Currently framework code is guarded under FIB_ALGO config option.
An idea is to enable it by default in the next couple of weeks.

The following algorithms are provided by default:
IPv4:
* bsearch4 (lockless binary search in a special IP array), tailored for
  small-fib (<16 routes)
* radix4_lockless (lockless immutable radix, re-created on every rtable change),
  tailored for small-fib (<1000 routes)
* radix4 (base system radix backend)
* dpdk_lpm4 (DPDK DIR24-8-based lookups), lockless datastrucure, optimized
  for large-fib (D27412)
IPv6:
* radix6_lockless (lockless immutable radix, re-created on every rtable change),
  tailed for small-fib (<1000 routes)
* radix6 (base system radix backend)
* dpdk_lpm6 (DPDK DIR24-8-based lookups), lockless datastrucure, optimized
  for large-fib (D27412)

Performance changes:
Micro benchmarks (I7-7660U, single-core lookups, 2048k dst, code in D27604):
IPv4:
8 routes:
  radix4: ~20mpps
  radix4_lockless: ~24.8mpps
  bsearch4: ~69mpps
  dpdk_lpm4: ~67 mpps
700k routes:
  radix4_lockless: 3.3mpps
  dpdk_lpm4: 46mpps

IPv6:
8 routes:
  radix6_lockless: ~20mpps
  dpdk_lpm6: ~70mpps
100k routes:
  radix6_lockless: 13.9mpps
  dpdk_lpm6: 57mpps

Forwarding benchmarks:
+ 10-15% IPv4 forwarding performance (small-fib, bsearch4)
+ 25% IPv4 forwarding performance (full-view, dpdk_lpm4)
+ 20% IPv6 forwarding performance (full-view, dpdk_lpm6)

Control:
Framwork adds the following runtime sysctls:

List algos
* net.route.algo.inet.algo_list: bsearch4, radix4_lockless, radix4
* net.route.algo.inet6.algo_list: radix6_lockless, radix6, dpdk_lpm6
Debug level (7=LOG_DEBUG, per-route)
net.route.algo.debug_level: 5
Algo selection (currently only for fib 0):
net.route.algo.inet.algo: bsearch4
net.route.algo.inet6.algo: radix6_lockless

Support for manually changing algos in non-default fib will be added
soon. Some sysctl names will be changed in the near future.

Differential Revision: https://reviews.freebsd.org/D27401

sys/conf/files

@@ -4178,6 +4178,7 @@ net/route/nhgrp_ctl.c		optional route_mpath
 net/route/nhop.c		standard
 net/route/nhop_ctl.c		standard
 net/route/nhop_utils.c		standard
+net/route/fib_algo.c		optional fib_algo
 net/route/route_ctl.c		standard
 net/route/route_ddb.c		optional ddb
 net/route/route_helpers.c	standard
@@ -4329,6 +4330,7 @@ netinet/in_debug.c		optional inet ddb
 netinet/in_kdtrace.c		optional inet | inet6
 netinet/ip_carp.c		optional inet carp | inet6 carp
 netinet/in_fib.c		optional inet
+netinet/in_fib_algo.c		optional inet fib_algo
 netinet/in_gif.c		optional gif inet | netgraph_gif inet
 netinet/ip_gre.c		optional gre inet
 netinet/ip_id.c			optional inet
@@ -4405,6 +4407,7 @@ netinet6/icmp6.c		optional inet6
 netinet6/in6.c			optional inet6
 netinet6/in6_cksum.c		optional inet6
 netinet6/in6_fib.c		optional inet6
+netinet6/in6_fib_algo.c		optional inet6 fib_algo
 netinet6/in6_gif.c		optional gif inet6 | netgraph_gif inet6
 netinet6/in6_ifattach.c		optional inet6
 netinet6/in6_jail.c		optional inet6

sys/conf/options

@@ -454,6 +454,7 @@ PCBGROUP		opt_pcbgroup.h
 PF_DEFAULT_TO_DROP	opt_pf.h
 ROUTE_MPATH		opt_route.h
 ROUTETABLES		opt_route.h
+FIB_ALGO		opt_route.h
 RSS			opt_rss.h
 SLIP_IFF_OPTS		opt_slip.h
 TCPDEBUG

sys/net/route.c

@@ -151,6 +151,14 @@ void
 rt_table_destroy(struct rib_head *rh)
 {
 
+	RIB_WLOCK(rh);
+	rh->rib_dying = true;
+	RIB_WUNLOCK(rh);
+
+#ifdef FIB_ALGO
+	fib_destroy_rib(rh);
+#endif
+
 	tmproutes_destroy(rh);
 
 	rn_walktree(&rh->rmhead.head, rt_freeentry, &rh->rmhead.head);