tipc: Update obsolete references to multicast link

Updates TIPC's broadcast link in a couple of places that were missed
during the transition from its former name ("multicast-link") to its
current name ("broadcast-link"). These changes are essentially cosmetic
and do not affect the overall operation of TIPC.

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