Fix error in "convectioncoefficient" ScheduleTypeLimit::units()

This fixes an error in ScheduleTypeLimits::units() for "convectioncoefficient". The IP and SI units appear to be switched based solely on the names of the method calls. I haven't looked too deep into this to make sure, but it definitely appears to be a bug. 

"convectioncoefficient" doesn't appear to be used (yet) in ScheduleTypeRegistrySingleton::ScheduleTypeRegistrySingleton() in ScheduleTypeRegistry.cpp so this might be why it has not be seen or fixed yet.

@macumber