s390/qeth: don't process empty bridge port events

[ Upstream commit 02472e28 ]

Discard events that don't contain any entries. This shouldn't happen,
but subsequent code relies on being able to use entry 0. So better
be safe than accessing garbage.

Fixes: b4d72c08

 ("qeth: bridgeport support - basic control")
Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Reviewed-by: Alexandra Winter <wintera@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>