s390/qeth: remove .do_ioctl() callback from driver discipline

s390/qeth: remove .do_ioctl() callback from driver discipline

With commit 18787eeebd71 ("qeth: use ndo_siocdevprivate") this callback
is now actually used to handle transport mode-specific _private_ ioctls.

We only have such ioctls for L3 devices. So wire up a L3-specific
.ndo_siocdevprivate() callback that handles those ioctls, and defers to
the core qeth_siocdevprivate() for all other private ioctls.

This takes the discipline one step closer to its original purpose of
providing an internal extension for the qeth_core_ccwgroup_driver.

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