tipc: Standardize exit logic for message rejection handling

Modifies the routine that handles the rejection of payload messages
so that it has a single exit point that frees up the rejected message,
thereby eliminating some duplicated code.

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