net: ipa: disable interrupt and NAPI after channel stop

Disable both the I/O completion interrupt and NAPI polling on a
channel *after* we successfully stop it rather than before.  This
ensures a completion occurring just before the channel is stopped
gets processed.

Enable NAPI polling and the interrupt *before* starting a channel
rather than after, to be symmetric.  A stopped channel won't
generate any completion interrupts anyway.

Enable NAPI before the interrupt and disable it afterward.

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