mod_transport: Make out-band message support optional
Created by: AndyJGraham
The goal of this change is to make out-band message support option through use of conditional compilation.
The compilation flag that was added is: BUILD_HAS_OUTBAND_MSG_SUPPORT
All platforms that use "mod_transport" have been updated to have this new flag by default.
Change-Id: I903f77ada1d61128ee4b76cb130cfe4fc4ff81ab