net: linux/skbuff.h: combine SKB_EXTENSIONS + KCOV handling

commit 97f53a0 upstream.

The previous Kconfig patch led to some other build errors as
reported by the 0day bot and my own overnight build testing.

These are all in <linux/skbuff.h> when KCOV is enabled but
SKB_EXTENSIONS is not enabled, so fix those by combining those conditions
in the header file.

Fixes: 6370cc3 ("net: add kcov handle to skb extensions")
Fixes: 85ce50d ("net: kcov: don't select SKB_EXTENSIONS when there is no NET")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reported-by: kernel test robot <lkp@intel.com>
Cc: Aleksandr Nogikh <nogikh@google.com>
Cc: Willem de Bruijn <willemb@google.com>
Acked-by: Florian Westphal <fw@strlen.de>
Link: https://lore.kernel.org/r/20201116212108.32465-1-rdunlap@infradead.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

include/linux/skbuff.h

@@ -4608,7 +4608,7 @@ static inline void skb_reset_redirect(struct sk_buff *skb)
 #endif
 }
 
-#ifdef CONFIG_KCOV
+#if IS_ENABLED(CONFIG_KCOV) && IS_ENABLED(CONFIG_SKB_EXTENSIONS)
 static inline void skb_set_kcov_handle(struct sk_buff *skb,
 				       const u64 kcov_handle)
 {
@@ -4636,7 +4636,7 @@ static inline u64 skb_get_kcov_handle(struct sk_buff *skb)
 static inline void skb_set_kcov_handle(struct sk_buff *skb,
 				       const u64 kcov_handle) { }
 static inline u64 skb_get_kcov_handle(struct sk_buff *skb) { return 0; }
-#endif /* CONFIG_KCOV */
+#endif /* CONFIG_KCOV && CONFIG_SKB_EXTENSIONS */
 
 #endif	/* __KERNEL__ */
 #endif	/* _LINUX_SKBUFF_H */