Fix PWM flickering during wifi connection (#8046)

[s-hadinger]

Description:

Fix #7851 allowed the PWM interrupt handler to keep phases constant between channels and avoid flickering.

Unfortunatel, under heavy interrupt load, at wifi connection, the interrupt handler struggles to keep PWM at correct levels. In case of an overshoot of the PWM cycle by more than 25%, the interrupt handler reverts to the previous behavior and favors PWM level instead of phases.
This minimizes flickering at wifi connection.

Related issue (if applicable): fixes #8046

Checklist:

• The pull request is done against the latest dev branch
• Only relevant files were touched
• Only one feature/fix was added per PR.
• The code change is tested and works on core Tasmota_core_stage
• The code change pass travis tests. Your PR cannot be merged unless tests pass
• I accept the CLA.