tipc: Don't create payload message using connection protocol routine

Modifies the logic that creates a connection termination payload
message so that it no longer (mis)uses a routine that creates a
connection protocol message. The revised code is now more easily
understood, and avoids setting several fields that are either not
present in payload messages or were being set more than once.

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