selftests: futex: Test sys_futex_waitv() timeout

Test if the futex_waitv timeout is working as expected, using the
supported clockid options.

Signed-off-by: André Almeida <andrealmeid@collabora.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210923171111.300673-21-andrealmeid@collabora.com