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: NPablo Neira Ayuso <pablo@netfilter.org>