Add a perform_ip_subnet_bcast() function that uses Linux netlink sockets to set the interface ip, subnet, and broadcast address simultaneously.
Add a perform_ip_subnet_bcast() function that uses Linux netlink sockets
to set the interface ip, subnet, and broadcast address simultaneously.

The advantage of this approach is that a single netlink notification
will be sent rather than multiple messages as the ip, subnet,
and broadcast address are set one at a time.

Currently this function is not used, as it will require a wire format
change that will be introduced in a subsequent commit.

niklata/ndhc