Floss: reroute libchrome logs to syslog

Currently, libchrome logs are discarded entirely. In this CL, we hijack
the messages and send them to syslog before they are gone.

Note that `TraceConf` needs to be set in `bt_stack.conf` before this
takes effect.

Bug: 279873537
Tag: #floss
Test: Build and verify
Change-Id: I9189946aed140dc185d8a8965609e57b31f1b1d8