tipc: Enhance cleanup of broadcast link when contact with node is lost

Enhances cleanup of broadcast link-related information when contact
with a node is lost.

1) All broadcast link-related cleanup now occurs only if the lost node
   was capable of communicating over the broadcast link.

2) Following cleanup, the lost node is marked as no longer supporting
   the broadcast link, ensuring that any remaining broadcast messages
   received from that node prior to the re-establishment of a normal
   communication link are ignored.

Thanks to Surya [Suryanarayana.Garlapati@emerson.com] for contributing
a prototype version of this patch.

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