tipc: Cosmetic changes to broadcast bearer send routine

Updates the comments in the broadcast bearer send routine to more
accurately describe the processing done by the routine. Also replaces
the improper use of a TIPC payload message error status symbol (in a place
that has nothing to do with such errors) with its numeric equivalent.

Signed-off-by: Allan Stephens <allan.stephens@windriver.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>