tcp: Update stale comment for MD5 in tcp_parse_options().

Since commit 9ea88a15 ("tcp: md5: check md5 signature without socket
lock"), the MD5 option is checked in tcp_v[46]_rcv().

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20230803224552.69398-3-kuniyu@amazon.com


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