af_unix: Do not use atomic ops for unix_sk(sk)->inflight.

When touching unix_sk(sk)->inflight, we are always under
spin_lock(&unix_gc_lock).

Let's convert unix_sk(sk)->inflight to the normal unsigned long.

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://lore.kernel.org/r/20240123170856.41348-3-kuniyu@amazon.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>