ctdb-common: Support "any" interface for pcap-based capture

ctdb-common: Support "any" interface for pcap-based capture

This uses Linux cooked capture link-layer headers.  See:

  https://www.tcpdump.org/linktypes/LINKTYPE_LINUX_SLL.html
  https://www.tcpdump.org/linktypes/LINKTYPE_LINUX_SLL2.html

The header type needs to be checked to ensure the protocol
type (i.e. ether type, for the protocols we might be interested in) is
meaningful.  The size of the header needs to be known so it can be
skipped, allowing the IP header to be found and parsed.

It would be possible to define support for DLT_LINUX_SLL2 if it is
missing.  However, if a platform is missing support in the header file
then it is almost certainly missing in the run-time library too.

Signed-off-by: Martin Schwenke <martin@meltin.net>
Reviewed-by: Amitay Isaacs <amitay@gmail.com>