net: ipa: don't thaw channel if error starting

If an error occurs starting a channel, don't "thaw" it.
We should assume the channel remains in a non-started state.

Update the comment in gsi_channel_stop(); calls to this function
are no longer retried.

Signed-off-by: Alex Elder <elder@linaro.org>
Acked-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>