Add helpers for normal inbound packet destination addresses

tap_ip_send() doesn't take a destination address, because it's specifically
for inbound packets, and the IP addresses of the guest/namespace are
already known to us.  Rather than open-coding this destination address
logic, make helper functions for it which will enable some later cleanups.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

tap.h

@@ -6,6 +6,9 @@
 #ifndef TAP_H
 #define TAP_H
 
+in_addr_t tap_ip4_daddr(const struct ctx *c);
+const struct in6_addr *tap_ip6_daddr(const struct ctx *c,
+				     const struct in6_addr *src);
 void tap_ip_send(const struct ctx *c, const struct in6_addr *src, uint8_t proto,
 		 const char *in, size_t len, uint32_t flow);
 int tap_send(const struct ctx *c, const void *data, size_t len, int vnet_pre);