lib: Fix FreeBSD build.

Various recent commits have introduced build failures on FreeBSD. This
patch fixes them.

Signed-off-by: Joe Stringer <joestringer@nicira.com>
Acked-by: Ben Pfaff <blp@nicira.com>
datapath: Remove redundant tcp_flags code.

These two cases used to be treated differently for IPv4/IPv6, but they
are now identical.

Signed-off-by: Joe Stringer <joestringer@nicira.com>
Acked-by: Jarno Rajahalme <jrajahalme@nicira.com>
Acked-by: Pravin B Shelar <pshelar@nicira.com>