lacp: fix regarding vm arg for vlib_time_now calls

lacp: fix regarding vm arg for vlib_time_now calls

Use thread-specific vlib_main_t *vm pointers to avoid problems with
different threads accessing the same vlib_main_t data structure.
This avoids assertion failure when vlib_time_now() is called with a vm
corresponding to a different thread.

Type: fix

Signed-off-by: Elias Rudberg <elias.rudberg@bahnhof.net>
Change-Id: I359596ecff86e03d57aa8d2330f77bf9a913485f