media: cec: core: not all messages were passed on when monitoring

The valid_la boolean is used to check if the destination logical
address is either 15 (broadcast) or our logical address. If it is
for another logical address, then only adapters that have the
CEC_CAP_MONITOR_ALL capability can pass it on.

However, it is also used to do more detailed validity checks,
such as whether the message was broadcast when it should have been
directed, or vice versa, in which case the message must be ignored
according to the spec. But that should not apply to monitoring.

Add a new bool that just checks the LA and nothing else.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>