UPSTREAM: wireguard: ratelimiter: disable timings test by default

A previous commit tried to make the ratelimiter timings test more
reliable but in the process made it less reliable on other
configurations. This is an impossible problem to solve without
increasingly ridiculous heuristics. And it's not even a problem that
actually needs to be solved in any comprehensive way, since this is only
ever used during development. So just cordon this off with a DEBUG_
ifdef, just like we do for the trie's randomized tests, so it can be
enabled while hacking on the code, and otherwise disabled in CI. In the
process we also revert 151c8e499f47.

Bug: 254441685
Fixes: 151c8e499f47 ("wireguard: ratelimiter: use hrtimer in selftest")
Fixes: e7096c131e51 ("net: WireGuard secure network tunnel")
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
(cherry picked from commit 684dec3cf45da2b0848298efae4adf3b2aeafeda)
Signed-off-by: Lee Jones <joneslee@google.com>
Change-Id: I2501d61983021de424564ef8e432cca0f51a60b0