netfilter: ebtables: add support for matching ICMP type and code

We already have ICMPv6 type/code matches. This adds support for IPv4 ICMP
matches in the same way.

Signed-off-by: Matthias Schiffer <mschiffer@universe-factory.net>
Acked-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>