tipc: manually inline net_start/stop, make assoc. vars static

Relocates network-related variables into the subsystem files where
they are now primarily used (following the recent rework of TIPC's
node table), and converts globals into locals where possible. Changes
the initialization of tipc_num_links from run-time to compile-time,
and eliminates the net_start routine that becomes empty as a result.
Also eliminates the corresponding net_stop routine by moving its
(trivial) content into the one location that called the routine.

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