Allow em_ipt to use addrtype for matching. Restrict the use only to
revision 1 which has IPv6 support. Since it's a NFPROTO_UNSPEC xt match
we use the user-specified nfproto for matching, in case it's unspecified
both v4/v6 will be matched by the rule.

v2: no changes, was patch 5 in v1
Signed-off-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>