ehea: Fix synchronization between HW and SW send queue

When memory is added to / removed from a partition via the Memory DLPAR
mechanism, the eHEA driver has to do a couple of things to reflect the
memory change in its own IO address translation tables. This involves
stopping and restarting the HW queues.
During this operation, it is possible that HW and SW pointer into these
queues get out of sync. This results in a situation where packets that
are attached to a send queue are not transmitted immediately, but
delayed until further X packets have been put on the queue.

This patch detects such loss of synchronization, and resets the ehea
port when needed.
Signed-off-by: Jan-Bernd Themann <themann@de.ibm.com>
Signed-off-by: Andre Detsch <adetsch@br.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>