rust_binder: wake epoll on self-work queued to poll thread

When a thread pushes work to its own todo list, InnerThread::push_work()
returns PushWorkRes::OkNotifyPoll if the thread uses epoll, but four
call sites in thread.rs discard this return value. As a result, a
non-blocking BC_* write that enqueues work onto the calling thread's
todo list without also reading will not wake epoll. Check the return
value and call self.process.notify_poll(false) when
PushWorkRes::OkNotifyPoll is returned.

This is similar to commit 97830f3c3088 ("binder: signal epoll threads of
self-work"), but in C Binder pending thread work also prevented
subsequent process work from waking epoll, causing a permanent hang,
which is not the case in Rust Binder. This means that in practice, it
merely delays notifications rather than completely failing to send them.

Cc: stable@kernel.org
Fixes: dbb17c9ea756 ("rust_binder: move (e)poll wait queue to Process")
Reported-by: Poil Zero <poilandgginchi@gmail.com>
Signed-off-by: Alice Ryhl <aliceryhl@google.com>
Link: https://patch.msgid.link/20261016-binder-poll-self-work-v1-1-c29c87d99abb@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>