Added separate CAN address for rack 2 PWM enables.

Added a second pair of CAN addresses for rack 2 AFE and INV PWM enables.

Testing today consisted of testing each rack from AFE-INV(openloop)-NPC(diodes)
up to 5kW with NHR 9200 load. This followed by AFE-INV(closedloop)-NPC(diodes)
individually to the load. After connecting the NPC outputs together, the load
was apply first slowly up to 5kW then a 0-5kW step change. Then 5-8kW followed
by a 0-8kW step change. Final increase up to 10kW then 0-10kW. A previous
modification had rack 1 NPC input inductors at 0.6mH and rack 2 at 2.07mH
which caused an imperfect power balance.

The rack 1 inductors were changed back to the original 2.07mH set and 0-10kW
test was redone showing better power balance. However, even with closed loop
inverter control the output of the two NPCs in diode-rectifier mode had
a significant voltage drop under load.