Use rx failsafe when baseflight failsafe is not enabled for s.bus

The current implementation ignores all rx packets on s.bus when the rx is in failsafe mode.
This might make sense when using the baseflight controlled failsafe, but when not I want to use the rx failsafe instead.
This change will still read the s.bus channels if baseflight failsafe is disabled and failsafe bit is set.