[AX25/NETROM]: Cleanup direct calls into IP stack

Get rid of the calls to ip_rcv and arp_rcv which were layering
violations anyway.  With those being replaced by netif_rx, less parts
of AX.25 and relatives depend on INET support actually being enabled.
This also will make PF_PACKET sockets work for IP and ARP packets
received over AX.25 and for IP packets over NET/ROM.

Signed-off-by: Ralf Baechle DL5RB <ralf@linux-mips.org>
Signed-off-by: David S. Miller <davem@davemloft.net>