ANDROID: scheduler: add vendor-specific wake flag

It comes with the commit efbb82d3b0db ("ANDROID: Add a vendor hook
that allow a module to modify the wake flag"). A vendor who want to
hook sock_def_readable can set this vendor-specific wake flag.

sock_def_readable ->
(vendor hook will call __wake_up_sync_key with a custom mode) ->
__wake_up_sync_key ->
(vendor hook changes wake_flags per the custom mode) ->
__wake_up_common -> default_wake_function

It is an Android-specific since it works with a vendor hook.

Bug: 189858948
Bug: 226256614
Bug: 263838089
Bug: 349225664
Signed-off-by: Namkyu Kim <namkyu78.kim@samsung.com>
Change-Id: Idc23c1c47f7d83b298c0b2560859f1ce2761fd85
(cherry picked from commit 4c1097df)
(cherry picked from commit 87b89ce8)
(cherry picked from commit ffb7f4ad)
Signed-off-by: Dongseok Yi <dseok.yi@samsung.com>