s390/qeth: make af_iucv TX notification call more robust

s390/qeth: make af_iucv TX notification call more robust

[ Upstream commit 34c7f50f7d0d36fa663c74aee39e25e912505320 ]

Calling into socket code is ugly already, at least check whether we are
dealing with the expected sk_family. Only looking at skb->protocol is
bound to cause troubles (consider eg. af_packet).

Fixes: b333293058aa ("qeth: add support for af_iucv HiperSockets transport")
Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>