net: socket: Change the protocol field for AF_PACKET sockets

In order to be compatible with Linux AF_PACKET socket calls, the
protocol field needs to be in network byte order.
So for example, if user wants to receive all packets, then the
protocol field needs to be set as "htons(ETH_P_ALL)".
See Linux manual page at
https://www.man7.org/linux/man-pages/man7/packet.7.html


for details.

Signed-off-by: Jukka Rissanen <jukka.rissanen@nordicsemi.no>