ehea: Fix kernel deadlock in DLPAR-mem processing

Port reset operations and memory add/remove operations need to
be serialized to avoid a kernel deadlock. The deadlock is caused
by calling the napi_disable() function twice.
Therefore we have to employ the dlpar_mem_lock in the ehea_reset_port
function as well

Signed-off-by: Jan-Bernd Themann <themann@de.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>