Reduce <sys/queue.h> pollution.

While <sys/sysctl.h> includes <sys/queue.h> unconditionally, it is only
actually used in code which is conditional on _KERNEL.  Make the #include
itself conditional as well, and fix userland code that uses <sys/queue.h>
for other purposes but relied on <sys/sysctl.h> to bring it in.

MFC after:	1 week

lib/libkvm/kvm_getswapinfo.c

@@ -33,6 +33,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/time.h>
 #include <sys/stat.h>
 #include <sys/blist.h>
+#include <sys/queue.h>
 #include <sys/sysctl.h>
 
 #include <vm/swap_pager.h>

lib/libmemstat/memstat.c

@@ -29,6 +29,7 @@
  */
 
 #include <sys/param.h>
+#include <sys/queue.h>
 #include <sys/sysctl.h>
 
 #include <err.h>

sys/sys/sysctl.h

@@ -38,7 +38,9 @@
 #ifndef _SYS_SYSCTL_H_
 #define	_SYS_SYSCTL_H_
 
+#ifdef _KERNEL
 #include <sys/queue.h>
+#endif
 
 struct thread;
 /*

usr.bin/systat/ifstat.c

@@ -32,6 +32,7 @@
 
 #include <sys/types.h>
 #include <sys/socket.h>
+#include <sys/queue.h>
 #include <sys/sysctl.h>
 #include <net/if.h>
 #include <net/if_mib.h>

usr.bin/systat/tcp.c

@@ -44,6 +44,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/param.h>
 #include <sys/types.h>
 #include <sys/socket.h>
+#include <sys/queue.h>
 #include <sys/sysctl.h>
 
 #include <netinet/in.h>

usr.sbin/route6d/route6d.c

@@ -39,6 +39,7 @@ static const char _rcsid[] = "$KAME: route6d.c,v 1.104 2003/10/31 00:30:20 itoju
 #include <sys/param.h>
 #include <sys/file.h>
 #include <sys/ioctl.h>
+#include <sys/queue.h>
 #include <sys/socket.h>
 #include <sys/sysctl.h>
 #include <sys/uio.h>

usr.sbin/rtadvd/rrenum.c

@@ -34,6 +34,7 @@
 #include <sys/types.h>
 #include <sys/param.h>
 #include <sys/ioctl.h>
+#include <sys/queue.h>
 #include <sys/socket.h>
 #include <sys/sysctl.h>