net: Un-hide lockdep_sock_is_held() for !LOCKDEP

Currently, variables used only within lockdep expressions are flagged
as unused, requiring that these variables' declarations be decorated
with either #ifdef or __maybe_unused.  This results in ugly code.
This commit therefore causes the lockdep_sock_is_held() function to be
visible even when lockdep is not enabled, thus removing the need for
these decorations.  This approach further relies on dead-code elimination
to remove any references to functions or variables that are not available
in non-lockdep kernels.
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

include/net/sock.h

@@ -1566,13 +1566,11 @@ do {									\
 	lockdep_init_map(&(sk)->sk_lock.dep_map, (name), (key), 0);	\
 } while (0)
 
-#ifdef CONFIG_LOCKDEP
 static inline bool lockdep_sock_is_held(const struct sock *sk)
 {
 	return lockdep_is_held(&sk->sk_lock) ||
 	       lockdep_is_held(&sk->sk_lock.slock);
 }
-#endif
 
 void lock_sock_nested(struct sock *sk, int subclass);