Reset TCP/IP connection with a '+' prefix

When running scrcpy with --tcpip=xx.xx.xx.xx, to make sure a new working
connection is established, it was first disconnected by a call to:

    adb disconnect <addr>

However, this caused all running instances connected to that address to
be killed. Running several instances of scrcpy on the same device is now
useful with virtual displays, so change the default behavior to NOT
disconnect.

To force a reconnection, a '+' prefix can be added:

    scrcpy --tcpip=+192.168.0.x

Fixes #5562 <https://github.com/Genymobile/scrcpy/issues/5562>