NET: hamradio: Fix IP over bpq encapsulation.

Since 1d5da757 (ax25: Stop using magic
neighbour cache operations.) any attempt to transmit IP packets over
a bpqether device will result in a message like "Dead loop on virtual
device bpq0, fix it urgently!"

Fix suggested by Eric W. Biederman <ebiederm@xmission.com>.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Cc: <stable@vger.kernel.org> # 4.1
Signed-off-by: David S. Miller <davem@davemloft.net>