ibmvnic: Report queue stops and restarts as debug output

It's not necessary to report each time a queue is stopped and restarted
as an informational message. Change that to be a debug message so that
it can be observed if needed but not printed by default.

Signed-off-by: Thomas Falcon <tlfalcon@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>