s390/ctcm: Avoid temporary allocation of struct qllc.

The size of struct qllc is 2 byte. The memory for is allocated,
initialized, used and deallocated a few lines later.

It is more efficient to avoid the allocation/free dance and assign the
values directly to skb's data part instead of using memcpy() for it.

Avoid an allocation of struct qllc and use the resulting skb pointer
instead.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
[jwi: remove a newline, reflow the commit msg]
Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>