Use const parameters for complex data types on log and trace messages.
The BGP code is littered with vector copies of parameters used for
logging; this is both wasteful and a burden to the programmer.

Change-Id: I9f214c0e29684d16bcb33b812b1270f22bac2b68
Merge "Use const parameters for complex data types on log and trace messages. The BGP code is littered with vector copies of parameters used for logging; this is both wasteful and a burden to the programmer."