tipc: Display meaningful peer interface name during link creation

Sets the peer interface portion of the name of a newly created link
endpoint to "unknown". This ensures that state and statistics information
can be properly displayed during the time between the link endpoint's
creation and the time handshaking with its peer is completed.

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