Replace the use of wall clock time with monotonically increasing

Replace the use of wall clock time with monotonically increasing
clock.  In general, gettimeofday() is not appropriate interface
when accounting for elasped time because it can go backward, in
which case the policy code could errornously consider the limit
as exceeded.

MFC after:	1 week
Reported by:	Mahesh Arumugam
Submitted by:	Dorr H. Clark via gnn
Sponsored by:	Citrix / NetScaler