USB: sierra: add support for Sierra Wireless MC7710

Just add new device id. 3G works fine, LTE not tested.

Signed-off-by: Anton Samokhvalov <pg83@yandex.ru>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>