Those libraries, routing message parsers, netlink message parsers,
berkeley packat filter are linux packet filter, are subsets and just for
the net package of standard library. It would be better keeping,
extending them at the net sub repository instead of here.

Updates golang/go#10150.

Change-Id: I1ca437bea2e2be7f7f8f6496d4db291629f49136
Reviewed-on: https://go-review.googlesource.com/7581Reviewed-by: Russ Cox <rsc@golang.org>
Reviewed-by: Rob Pike <r@golang.org>