tipc: Set name lookup scope field properly in all data messages

Ensures that all outgoing data messages have the "name lookup scope"
field of their header set correctly; that is, named multicast messages
now specify cluster-wide name lookup, while messages not using TIPC
naming zero out the lookup field.  (Previously, the lookup scope specified
for these types of messages was inherited from the last message sent
by the sending port.)

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