tipc: Update commenting in TIPC API

Eliminate comments in TIPC's main API files that are either obsolete,
incorrect, misleading, or unhelpful.  It also adds in one new comment.

Signed-off-by: Allan Stephens <allan.stephens@windriver.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>