docs/library/ubluetooth.rst: Add docs for L2CAP channels.
docs/library/ubluetooth.rst: Add docs for L2CAP channels.

Signed-off-by: Jim Mussared <e84f5c941266186d0c97dcc873413469b954847e@gmail.com>

henriknelson/micropython,adafruit/circuitpython,henriknelson/micropython,adafruit/circuitpython,MrSurly/micropython,bvernoux/micropython,MrSurly/micropython,bvernoux/micropython,MrSurly/micropython,bvernoux/micropython,adafruit/circuitpython,adafruit/circuitpython,bvernoux/micropython,MrSurly/micropython,MrSurly/micropython,henriknelson/micropython,adafruit/circuitpython,henriknelson/micropython,adafruit/circuitpython,bvernoux/micropython,henriknelson/micropython