net: page_pool, skbuff: make skb_mark_for_recycle() always available

skb_mark_for_recycle() is guarded with CONFIG_PAGE_POOL, this creates
unneeded complication when using it in the generic code. For now, it's
only used in the drivers always selecting Page Pool, so this works.
Move the guards so that preprocessor will cut out only the operation
itself and the function will still be a noop on !PAGE_POOL systems,
but available there as well.
No functional changes.

Reported-by: kernel test robot <lkp@intel.com>
Link: https://lore.kernel.org/oe-kbuild-all/202303020342.Wi2PRFFH-lkp@intel.com
Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com>
Link: https://lore.kernel.org/r/20230313215553.1045175-3-aleksander.lobakin@intel.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

include/linux/skbuff.h

@@ -5069,12 +5069,12 @@ static inline u64 skb_get_kcov_handle(struct sk_buff *skb)
 #endif
 }
 
-#ifdef CONFIG_PAGE_POOL
 static inline void skb_mark_for_recycle(struct sk_buff *skb)
 {
+#ifdef CONFIG_PAGE_POOL
 	skb->pp_recycle = 1;
-}
 #endif
+}
 
 #endif	/* __KERNEL__ */
 #endif	/* _LINUX_SKBUFF_H */