net: ipa: verify command channel TLV count

In commit 8797972a ("net: ipa: remove command info pool"), the
maximum number of IPA commands that would be sent in a single
transaction was defined.  That number can't exceed the size of the
TLV FIFO on the command channel, and we can check that at runtime.

To add this check, pass a new flag to gsi_channel_data_valid() to
indicate the channel being checked is being used for IPA commands.
Knowing that we can also verify the channel direction is correct.

Use a new local variable that refers to the command-specific portion
of the data being checked.

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>