epoll keyed wakeups: teach epoll about hints coming with the wakeup key

epoll keyed wakeups: teach epoll about hints coming with the wakeup key

Use the events hint now sent by some devices, to avoid unnecessary wakeups
for events that are of no interest for the caller.  This code handles both
devices that are sending keyed events, and the ones that are not (and
event the ones that sometimes send events, and sometimes don't).

[[email protected]: coding-style fixes]
Signed-off-by: Davide Libenzi <[email protected]>
Cc: Alan Cox <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: David Miller <[email protected]>
Cc: William Lee Irwin III <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>