tests: Avoid IPv4-translated IPv6 address in sockettest

getnameinfo on macOS formats certain IPv6 addresses as IPv4-translated
addresses. The following pattern has been observed:
  ::ffff is formated as ::0.0.255.255
  ::fffe is formated as ::0.0.255.254
  ::ffff:0 is formated as ::255.255.0.0
  ::fffe:0 is formated as ::255.254.0.0
  ::ffff:0:0 is formated as ::ffff:0.0.0.0
  ::fffe:0:0 is formated as ::fffe:0:0
  ::ffff:0:0:0 is formated as ::ffff:0:0:0

The getnameinfo behavior causes a failure for:
  DO_TEST_PARSE_AND_FORMAT("::ffff", AF_UNSPEC, true);

Use non-ambigious IPv6 for parse/format testing.
Signed-off-by: NRoman Bolshakov <r.bolshakov@yadro.com>

tests/sockettest.c

@@ -378,7 +378,7 @@ mymain(void)
     DO_TEST_PARSE_AND_FORMAT("::1", AF_INET, false);
     DO_TEST_PARSE_AND_FORMAT("::1", AF_INET6, true);
     DO_TEST_PARSE_AND_FORMAT("::1", AF_UNIX, false);
-    DO_TEST_PARSE_AND_FORMAT("::ffff", AF_UNSPEC, true);
+    DO_TEST_PARSE_AND_FORMAT("::fffe:0:0", AF_UNSPEC, true);
 
     /* tests that specify a network that should contain the range */
     DO_TEST_RANGE("192.168.122.1", "192.168.122.1", "192.168.122.1", 24, 1, true);