net/mbedtls_net_connect: Preventing double close problem

In the test examples and real usage scenarios, 'mbedtls_net_free' is called after 'mbedtls_net_connect' fails, which will cause the problem of double close the same fd. It is possible to close this closed fd which has been applied by other link.

Signed-off-by: makejian <[email protected]>

library/net_sockets.c

@@ -196,6 +196,7 @@ int mbedtls_net_connect(mbedtls_net_context *ctx, const char *host,
         }
 
         close(ctx->fd);
+        ctx->fd = -1;
         ret = MBEDTLS_ERR_NET_CONNECT_FAILED;
     }