tests: Fix message for IP parse/format failures

Confusing message is printed when a parse/format sockettest fails. E.g.
there's a test that parses/formats ::ffff and the format fails like that:
  38) Test format ::ffff family AF_UNSPEC ...
  Offset 2
  Expect [0.0.255.255]
  Actual [ffff]

It should be instead:
  38) Test format ::ffff family AF_UNSPEC ...
  Offset 2
  Expect [ffff]
  Actual [0.0.255.255]
Signed-off-by: NRoman Bolshakov <r.bolshakov@yadro.com>
Reviewed-by: NAndrea Bolognani <abologna@redhat.com>

tests/sockettest.c

@@ -50,7 +50,7 @@ static int testFormat(virSocketAddr *addr, const char *addrstr, bool pass)
         return pass ? -1 : 0;
 
     if (STRNEQ(newaddrstr, addrstr)) {
-        virTestDifference(stderr, newaddrstr, addrstr);
+        virTestDifference(stderr, addrstr, newaddrstr);
         VIR_FREE(newaddrstr);
         return pass ? -1 : 0;
     } else {