The WMI command tx credit request/return period is impacted
by host CPU loading/scheduling. For a real world case, when
at most 90 WMI commands are queued, and the period is 30ms,
at least 2.7s is needed, so set timeout to 4s for safety margin.
Change-Id: Ice444946292cd4d3cb82f1672a157d3858ac8c5e
CRs-Fixed: 2875205