net: ipa: introduce gsi_channel_stop_retry()

Create a new helper function that encapsulates issuing a set of
channel stop commands, retrying if appropriate, with a short delay
between attempts.

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