hamradio: fix issue of dev reference count leakage in bpq_device_event()

When following tests are performed, it will cause dev reference counting
leakage.
a)ip link add bond2 type bond mode balance-rr
b)ip link set bond2 up
c)ifenslave -f bond2 rose1
d)ip link del bond2

When new bond device is created, the default type of the bond device is
ether. And the bond device is up, bpq_device_event() receives the message
and creates a new bpq device. In this case, the reference count value of
dev is hold once. But after "ifenslave -f bond2 rose1" command is
executed, the type of the bond device is changed to rose. When the bond
device is unregistered, bpq_device_event() will not put the dev reference
count.

Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Signed-off-by: Zhengchao Shao <shaozhengchao@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>