posix-timers: Handle the timer_[re]arm() return value

posix-timers: Handle the timer_[re]arm() return value

The [re]arm callbacks will return true when the timer was queued and false
if it was already expired at enqueue time.

In both cases the call sites can trivially queue the signal right there,
when the timer was already expired. That avoids a full round trip through
the hrtimer interrupt.

Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260408114952.198028466@kernel.org