bpf: Print function name in addition to function id

The verifier currently prints raw function ids when printing CALL
instructions or when complaining:

	5: (85) call 23
	unknown func 23

print a meaningful function name instead:

	5: (85) call bpf_redirect#23
	unknown func bpf_redirect#23

Moves the function documentation to a single comment and renames all
helpers names in the list to conform to the bpf_ prefix notation so
they can be greped in the kernel source.

Signed-off-by: Thomas Graf <[email protected]>
Acked-by: Daniel Borkmann <[email protected]>
Acked-by: Alexei Starovoitov <[email protected]>
Signed-off-by: David S. Miller <[email protected]>