netfilter: nfnetlink: relax strict multicast group check from netlink_bind

commit 62924af247e95de7041a6d6f2d06cdd05152e2dc upstream.

Relax the checking that was introduced in 97840cb6 ("netfilter:
nfnetlink: fix insufficient validation in nfnetlink_bind") when the
subscription bitmask is used. Existing userspace code code may request
to listen to all of the existing netlink groups by setting an all to one
subscription group bitmask. Netlink already validates subscription via
setsockopt() for us.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>