Enable chains with names having a known prefix

Enable chains with names having a known prefix

This patch enables chains that have a known prefix in their name.
Known prefixes are: 'ipv4', 'ipv6', 'arp', 'rarp'. All prefixes
are also protocols that can be evaluated on the ebtables level.

Following the prefix they will be automatically connected to an interface's
'root' chain and jumped into following the protocol they evaluate, i.e.,
a table 'arp-xyz' will be accessed from the root table using

ebtables -t nat -A <iface root table> -p arp -j I-<ifname>-arp-xyz

thus generating a 'root' chain like this one here:

Bridge chain: libvirt-O-vnet0, entries: 5, policy: ACCEPT
-p IPv4 -j O-vnet0-ipv4
-p ARP -j O-vnet0-arp
-p 0x8035 -j O-vnet0-rarp
-p ARP -j O-vnet0-arp-xyz
-j DROP

where the chain 'arp-xyz' is accessed for filtering of ARP packets.

Signed-off-by: Stefan Berger <stefanb@linux.vnet.ibm.com>