Netlink socket parsers

Netlink is, basically, an API used to transfer information between kernel and user-space processes. It consists on a standard sockets-based interface for user-space processes and an internal kernel API for kernel modules. The general idea would be to add netlink messages parsing support in strace. It could be very useful for network debug or tracing.

After this work, more netlink family protocols can be added (NETLINK_ROUTE, NETLINK_FIREWALL ...).