ManualControl: block race condition for arming on switch

In the case of arming on a switch, if the person turned off the
transmitter and the switch went to the arm position before the
connected flag went false, they could have an arm event that was
not desired. The disarm timeout would kick in after this.
Merge pull request #1095 from peabody124/switch_race

ManualControl: block race condition for arming on switch