net: mhi: Fix unexpected queue wake

This patch checks that MHI queue is not full before waking up the net
queue. This fix sporadic MHI queueing issues in xmit. Indeed xmit and
its symmetric complete callback (ul_callback) can run concurently, it
is then not safe to unconditionnaly waking the queue in the callback
without checking queue fullness.

Fixes: 3ffec6a1 ("net: Add mhi-net driver")
Signed-off-by: Loic Poulain <loic.poulain@linaro.org>
Link: https://lore.kernel.org/r/1607599507-5879-1-git-send-email-loic.poulain@linaro.org


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