net: sockets: Remove support for AF_PACKET/IPPROTO_RAW combination

IPPROTO_RAW is not a valid protocol type for AF_PACKET sockets, which
should only use IEEE 802.3 protocol numbers. Therefore remove support
for this type of sockets.

As an alternative, users can use AF_PACKET/SOCK_DGRAM or
AF_INET(6)/SOCK_RAW, depending on the actual use case.

Signed-off-by: Robert Lubos <robert.lubos@nordicsemi.no>