Before this commit, OSCSelectObserver would read the feedback value when
it was created, but then never update it anymore. In practice, the
OSCSelectObserver is created on startup, and when the surface connects
and configures feeback, this value is not applied.
For example, when sending `/set_surface` with a feedback value of
4 (Send SSID as path extension), `/strip/*` would get their ssid put
into the path, but `/select/plugin/*` messages would not have their
parameter id in the path. When setting the corresponding checkbox in the
default feedback preferences, it is applied as expected.
This commit passes the new feedback value to the OSCSelectObserver
instance whenever it changes, which ensures the value is applied as
expected.
142fa9f55d