af_unix: Replace BUG_ON() with WARN_ON_ONCE().

af_unix: Replace BUG_ON() with WARN_ON_ONCE().

commit d0f6dc26346863e1f4a23117f5468614e54df064 upstream.

This is a prep patch for the last patch in this series so that
checkpatch will not warn about BUG_ON().

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Acked-by: Jens Axboe <axboe@kernel.dk>
Link: https://lore.kernel.org/r/20240129190435.57228-2-kuniyu@amazon.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Lee Jones <lee@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>