tipc: take lock while updating node network address

The routine that changes the node's network address now takes TIPC's
network lock in write mode while the main address variable and associated
data structures are being changed; this is needed to ensure that the
link subsystem won't attempt to send a message off-node until the sending
port's message header template has been updated with the node's new
network address.

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