Fix bug where maximum provider limit was not being reflected

The limit of 5 providers had two issues, one it did not
reserve one slot for primary which meant that you could
enable 6 and also even though it wouldn't save and would
show an error when you hit that limit the toggle was not
reset which made it look like it was enabled.

Test: on device + unit
Bug: 324426504
Change-Id: Ibec4efd6394835729869194181161fe8ae743e76