Take some of the mystery out of who does what by

Take some of the mystery out of who does what by
renaming "if_register_bpf()" to "get_bpf_sock()",
"if_register_send()" to "get_udp_sock()" and
"if_register_receive()" to "configure_bpf_sock()".

Pull back interface_info knowledge and just pass
the interface name, rdomain and bpf socket fd as
required.