net/lapb: re-send packets on timeout

Actually re-send packets when the T1 timer runs out. This fixes a bug
where packets are waiting on the write queue until disconnection when
no other traffic is outstanding.

Signed-off-by: Josselin Costanzi <josselin.costanzi@mobile-devices.fr>
Signed-off-by: Maxime Jayat <maxime.jayat@mobile-devices.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>