net: __lock_sock() can be static

After commit 6511882cdd82 ("mptcp: allocate fwd memory separately
on the rx and tx path") __lock_sock() can be static again.

Make sure __lock_sock() is not inlined, so that lock_sock_nested()
no longer needs a stack canary.

Add a noinline attribute on lock_sock_nested() so that calls
to lock_sock() from net/core/sock.c are not inlined,
none of them are fast path to deserve that:

 - sockopt_lock_sock()
 - sock_set_reuseport()
 - sock_set_reuseaddr()
 - sock_set_mark()
 - sock_set_keepalive()
 - sock_no_linger()
 - sock_bindtoindex()
 - sk_wait_data()
 - sock_set_rcvbuf()

$ scripts/bloat-o-meter -t vmlinux.old vmlinux
add/remove: 0/0 grow/shrink: 0/3 up/down: 0/-312 (-312)
Function                                     old     new   delta
__lock_sock                                  192     188      -4
__lock_sock_fast                             239      86    -153
lock_sock_nested                             227      72    -155
Total: Before=24888707, After=24888395, chg -0.00%

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20260223092716.3673939-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>