src: allow filtering on L2 header in inet family

src: allow filtering on L2 header in inet family

Error: conflicting protocols specified: inet vs. ether
tcp dport 22 iiftype ether ether saddr 00:0f:54:0c:11:4
                                   ^^^^^^^^^^^

This allows the implicit inet proto dependency to get replaced
by an ethernet one.

This is possible since by the time we detect the conflict the
meta dependency for the network protocol has already been added.

So we only need to add another dependency on the Linklayer frame type.

Closes: http://bugzilla.netfilter.org/show_bug.cgi?id=981
Acked-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Florian Westphal <fw@strlen.de>