tftpd: Gracefully skip tests if networking is not enabled.

[des]

Summary

Sponsored by: Klara, Inc.

libexec/tftpd/tests/functional.c

if (protocol == PF_INET) {
                 addr6.sin6_family = PF_INET6;
                 addr6.sin6_port = htons(port);
                 server_addr = (struct sockaddr*)&addr6;
         }
 
         ATF_REQUIRE_EQ(getcwd(pwd, sizeof(pwd)), pwd);
         
         /* Must bind(2) pre-fork so it happens before the client's send(2) */
-        ATF_REQUIRE((server_s = socket(protocol, SOCK_DGRAM, 0)) > 0);
+        server_s = socket(protocol, SOCK_DGRAM, 0);
+        if (server_s < 0 && errno == EAFNOSUPPORT) {
+                atf_tc_skip("This test requires IPv%d support",
+                    protocol == PF_INET ? 4 : 6);
+        }
+        ATF_REQUIRE_MSG(server_s >= 0,
+            "socket failed with error %s", strerror(errno));
         ATF_REQUIRE_EQ_MSG(bind(server_s, server_addr, len), 0,
             "bind failed with error %s", strerror(errno));
 
         pid = fork();
         switch (pid) {
         case -1:
                 atf_tc_fail("fork failed");
                 break;