net/smc: move testlink work to system work queue

The testlink work waits for a response to the testlink request and
blocks the single threaded llc_wq. This type of work does not have to be
serialized and can be moved to the system work queue.

Signed-off-by: Karsten Graul <kgraul@linux.ibm.com>
Reviewed-by: Ursula Braun <ubraun@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>