s390/qeth: relax locking for ipato config data

card->ipato is currently protected by the conf_mutex. But most users
also hold the ip_lock - in particular qeth_l3_add_ip().

So slightly expand the sections under ip_lock in a few places (to
effectively cover a few error & no-op cases), and then drop the
conf_mutex where it's no longer needed.

Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>