test: make NSS IPv4 tuple bounds explicit

gaih_addrtuple.addr has room for an IPv6 address, while IPv4 uses only
the first struct in_addr. Express the remaining range directly in terms
of that type so static analysis can prove the access remains within the
array.

CID#1663899

Follow-up for 2d85bba6b9

src/test/test-nss-hosts.c

@@ -74,8 +74,8 @@ static void assert_myhostname_gaih_addrtuples(const struct gaih_addrtuple *tuple
         for (const struct gaih_addrtuple *it = tuples; it; it = it->next)
                 if (it->family == AF_INET)
                         assert_se(memeqzero(
-                                        (const uint8_t*) it->addr + FAMILY_ADDRESS_SIZE(AF_INET),
-                                        sizeof(it->addr) - FAMILY_ADDRESS_SIZE(AF_INET)));
+                                        (const uint8_t*) it->addr + sizeof(struct in_addr),
+                                        sizeof(it->addr) - sizeof(struct in_addr)));
 }
 
 static void print_struct_hostent(struct hostent *host, const char *canon) {