net: ipa: begin simplifying TX queue stop

There are a number of flags used in the IPA driver to attempt to
manage race conditions that can occur between runtime resume and
netdev transmit.  If we disable TX before requesting power, we can
avoid these races entirely, simplifying things considerably.

This patch implements the main change, disabling transmit always in
the net_device->ndo_start_xmit() callback, then re-enabling it again
whenever we find power is active (or when we drop the skb).

The patches that follow will refactor the "old" code to the point
that most of it can be eliminated.

Signed-off-by: Alex Elder <elder@linaro.org>
Link: https://lore.kernel.org/r/20240130192305.250915-3-elder@linaro.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>