tty: n_smux: Trigger TX worker after wakeup

After completing a wakeup, trigger the TX worker to start sending
pending data.

Without the fix, the TX worker will wait until either other activity or
a power-down transmit before sending pending TX data.

Change-Id: Ica90b35d9a3169992db49ff493f783c27a2989da
Signed-off-by: Eric Holmberg <eholmber@codeaurora.org>