tests/qtest/migration-helpers: Don't dup argument to qdict_put_str()

In migrate_set_ports() we call qdict_put_str() with a value string
which we g_strdup(). However qdict_put_str() takes a copy of the
value string, it doesn't take ownership of it, so the g_strdup()
only results in a leak:

Direct leak of 6 byte(s) in 1 object(s) allocated from:
    #0 0x56298023713e in malloc (/mnt/nvmedisk/linaro/qemu-from-laptop/qemu/build/asan/tests/qtest/migration-test+0x22f13e) (BuildId: b2b9174a5a54707a7f76bca51cdc95d2aa08bac1)
    #1 0x7fba0ad39738 in g_malloc debian/build/deb/../../../glib/gmem.c:128:13
    #2 0x7fba0ad4e583 in g_strdup debian/build/deb/../../../glib/gstrfuncs.c:361:17
    #3 0x56298036b16e in migrate_set_ports tests/qtest/migration-helpers.c:145:49
    #4 0x56298036ad1c in migrate_qmp tests/qtest/migration-helpers.c:228:9
    #5 0x56298035b3dd in test_precopy_common tests/qtest/migration-test.c:1820:5
    #6 0x5629803549dc in test_multifd_tcp_channels_none tests/qtest/migration-test.c:3077:5
    #7 0x56298036d427 in migration_test_wrapper tests/qtest/migration-helpers.c:456:5

Drop the unnecessary g_strdup() call.

Signed-off-by: Peter Maydell <[email protected]>
Reviewed-by: Fabiano Rosas <[email protected]>
Signed-off-by: Fabiano Rosas <[email protected]>

tests/qtest/migration-helpers.c

@@ -142,7 +142,7 @@ static void migrate_set_ports(QTestState *to, QList *channel_list)
             qdict_haskey(addr, "port") &&
             (strcmp(qdict_get_str(addrdict, "port"), "0") == 0)) {
                 addr_port = qdict_get_str(addr, "port");
-                qdict_put_str(addrdict, "port", g_strdup(addr_port));
+                qdict_put_str(addrdict, "port", addr_port);
         }
     }