l2tpv3: fix possible double free

freeaddrinfo(result) does not assign result = NULL, after frees it.
There will be a double free when it goes error case.
It is reported by covertiy.
Reviewed-by: NGonglei <arei.gonglei@huawei.com>
Cc: qemu-stable@nongnu.org
Signed-off-by: Nzhanghailiang <zhang.zhanghailiang@huawei.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

net/l2tpv3.c

@@ -660,7 +660,6 @@ int net_init_l2tpv3(const NetClientOptions *opts,
     if (fd == -1) {
         fd = -errno;
         error_report("l2tpv3_open : socket creation failed, errno = %d", -fd);
-        freeaddrinfo(result);
         goto outerr;
     }
     if (bind(fd, (struct sockaddr *) result->ai_addr, result->ai_addrlen)) {