net/9p: replace p9_poll_task with a work
net/9p: replace p9_poll_task with a work

Now that cmwq can handle high concurrency, it's more efficient to use
work than a dedicated kthread.  Convert p9_poll_proc() to a work
function for p9_poll_work and make p9_pollwake() schedule it on each
poll event.  The work is sync flushed on module exit.

Signed-off-by: Tejun Heo <546b05909706652891a87f7bfe385ae147f61f91@kernel.org>
Cc: Eric Van Hensbergen <f6aaec02cb2023b586fda1596c965a5752b892b4@gmail.com>
Cc: Ron Minnich <f569d0af9a3481c4007b95c7180d6c41009f2513@sandia.gov>
Cc: Latchesar Ionkov <1cce15653918254946894aae1b185a0680390953@ionkov.net>
Cc: b15a25546bc7bbb5fff02db92deed56aac7f44ec@lists.sourceforge.net

KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas