Use typing to reduce chances of IPv4 endianness errors

We recently corrected some errors handling the endianness of IPv4
addresses.  These are very easy errors to make since although we mostly
store them in network endianness, we sometimes need to manipulate them in
host endianness.

To reduce the chances of making such mistakes again, change to always using
a (struct in_addr) instead of a bare in_addr_t or uint32_t to store network
endian addresses.  This makes it harder to accidentally do arithmetic or
comparisons on such addresses as if they were host endian.

We introduce a number of IN4_IS_ADDR_*() helpers to make it easier to
directly work with struct in_addr values.  This has the additional benefit
of making the IPv4 and IPv6 paths more visually similar.

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

util.h

@@ -69,8 +69,16 @@
 #define MAC_ZERO		((uint8_t [ETH_ALEN]){ 0 })
 #define MAC_IS_ZERO(addr)	(!memcmp((addr), MAC_ZERO, ETH_ALEN))
 
-#define IPV4_IS_LOOPBACK(addr)						\
-	((addr) >> IN_CLASSA_NSHIFT == IN_LOOPBACKNET)
+#define IN4_IS_ADDR_UNSPECIFIED(a) \
+	((a)->s_addr == htonl(INADDR_ANY))
+#define IN4_IS_ADDR_BROADCAST(a) \
+	((a)->s_addr == htonl(INADDR_BROADCAST))
+#define IN4_IS_ADDR_LOOPBACK(a) \
+	(ntohl((a)->s_addr) >> IN_CLASSA_NSHIFT == IN_LOOPBACKNET)
+#define IN4_IS_ADDR_MULTICAST(a) \
+	(IN_MULTICAST(ntohl((a)->s_addr)))
+#define IN4_ARE_ADDR_EQUAL(a, b) \
+	(((struct in_addr *)(a))->s_addr == ((struct in_addr *)b)->s_addr)
 
 #define NS_FN_STACK_SIZE	(RLIMIT_STACK_VAL * 1024 / 8)
 #define NS_CALL(fn, arg)						\