bt/bt_bluez: Implement retry if rfcomm sockets are busy

bt/bt_bluez: Implement retry if rfcomm sockets are busy

There are cases where the connect() call returns EBUSY when trying to
connect to a device. This has been observed when sampling an RDTech
UM24C. In this case, scanning the device works fine. However, when
sampling the device, Sigrok first scans the device, then closes the
connection and re-opens it to sample the device. If the close/open
calls happen in close successions, the Bluetooth stack sometimes
returns EBUSY.

Work around this issue by retrying if the connect() returns EBUSY.

Signed-off-by: Andreas Sandberg <redacted>