With these changes, dial up Zephyr application/driver can use
socket(AF_PACKET, SOCK_RAW, IPPROTO_RAW) for creating
a socket for sending/receiving data to/from ppp net link, i.e.
packet is going to/from PPP L2.
Signed-off-by: Jani Hirsimäki <jani.hirsimaki@nordicsemi.no>