genetlink: make info in GENL_REQ_ATTR_CHECK() const

Make the local variable in GENL_REQ_ATTR_CHECK() const.
genl_info_dump() returns a const pointer, so the macro
is currently hard to use in genl dumps.

Link: https://lore.kernel.org/r/20240222222819.156320-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

include/net/genetlink.h

@@ -153,7 +153,7 @@ static inline void *genl_info_userhdr(const struct genl_info *info)
 
 /* Report that a root attribute is missing */
 #define GENL_REQ_ATTR_CHECK(info, attr) ({				\
-	struct genl_info *__info = (info);				\
+	const struct genl_info *__info = (info);			\
 									\
 	NL_REQ_ATTR_CHECK(__info->extack, NULL, __info->attrs, (attr)); \
 })