[TIPC]: Removal of message header option code

This patch removes code associated with optional, user-specified
fields of the TIPC message header.  Such fields were never
utilized by TIPC, and have now been removed from the protocol
specification.

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