If several devices are connected (as listed by `adb devices`), it was
necessary to provide the explicit serial via -s/--serial.
If only one device is connected via USB (respectively, via TCP/IP), it
might be convenient to select it automatically. For this purpose, two
new options are introduced:
- -U/--select-usb: select the single device connected over USB
- -T/--select-tcpip: select the single device connected over TCP/IP
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