Fix spammy logging for route discovery prefs notifications

This change is a (mostly) non-functional change to improve logging
when the binder transaction to notify a manager of a route discovery
preference change.

Bug: 360129098
Test: Manual simple casting flow using routing demo app
Flag: EXEMPT refactor

Change-Id: Ibee1a2431c2c937bc0aaefb9fc1e451b97dd8148