once: use __section(".data.once")

.data.once contains nicely packed bool variables.
It is used already by DO_ONCE_LITE().

Using it also in DO_ONCE() removes holes in .data section.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

include/linux/once.h

@@ -38,7 +38,7 @@ void __do_once_done(bool *done, struct static_key_true *once_key,
 #define DO_ONCE(func, ...)						     \
 	({								     \
 		bool ___ret = false;					     \
-		static bool ___done = false;				     \
+		static bool __section(".data.once") ___done = false;	     \
 		static DEFINE_STATIC_KEY_TRUE(___once_key);		     \
 		if (static_branch_unlikely(&___once_key)) {		     \
 			unsigned long ___flags;				     \