gro: add combined call_gro_receive() + INDIRECT_CALL_INET() helper

call_gro_receive() is used to limit GRO recursion, but it works only
with callback pointers.
There's a combined version of call_gro_receive() + INDIRECT_CALL_2()
in <net/inet_common.h>, but it doesn't check for IPv6 modularity.
Add a similar new helper to cover both of these. It can and will be
used to avoid retpoline overhead when IP header lies behind another
offloaded proto.

Signed-off-by: Alexander Lobakin <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/net/gro.h

···
 INDIRECT_CALLABLE_DECLARE(struct sk_buff *inet_gro_receive(struct list_head *,
 							   struct sk_buff *));
 INDIRECT_CALLABLE_DECLARE(int inet_gro_complete(struct sk_buff *, int));
+
+#define indirect_call_gro_receive_inet(cb, f2, f1, head, skb)	\
+({								\
+	unlikely(gro_recursion_inc_test(skb)) ?			\
+		NAPI_GRO_CB(skb)->flush |= 1, NULL :		\
+		INDIRECT_CALL_INET(cb, f2, f1, head, skb);	\
+})
+
 #endif /* _NET_IPV6_GRO_H */