net/tipc: fix all function Return: notation

Fix Return: kernel-doc notation in all net/tipc/ source files.
Also keep ReST list notation intact for output formatting.
Fix a few typos in comments.

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>