s390/qeth: trust non-IP cast type in qeth_l3_fill_header()

When building the L3 HW header for non-IP packets, trust the cast type
that was passed as parameter. qeth_l3_get_cast_type() has most likely
also used h_dest to determine the cast type, so we get the same
result, and can remove that duplicated code.
In the unlikely case that we would get a _different_ cast type, then
that's based off a route lookup and should be considered authoritative.

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