Nissan: allow B drive mode for Nissan Leaf

[cellfreak]

Add B ( Battery save ) drive mode for Nissan Leaf - selfdrive/car/nissan/interface.py

Line 50 - events = self.create_common_events(ret, extra_gears=[car.CarState.GearShifter.brake])

Road test successful - https://connect.comma.ai/0b17985326a570c4/1691100300431/1691100676848

[cellfreak]

cd /data && rm -rf openpilot && git clone --recursive https://github.com/cellfreak/openpilot -b master && sudo reboot

Ran on my Comma Three with no issues.

2019 Nissan Leaf SL Plus

[cellfreak]

B mode: ‘B mode’ enhances the driving range and improves regenerative braking efficiency.
D mode: the ‘D’ mode is significantly more responsive during acceleration and provides maximum EV performance. For drivers looking for an ideal driving experience and full EV perks, D mode is for you.
B mode with Eco: Great for downhill driving due to better regenerative braking; it also decreases required braking to reduce wear and tear on the vehicle.
D mode with Eco: Reduces energy consumption by moderating the AC unit and reducing responsiveness to acceleration; this is the best everyday driving mode.

[sshane]

Checked and this mode is only in the leaf DBC, so we can be sure that it will never occur on other cars