Delay DIAL cmd to RIL after sending SWITCH_WAITING_OR_HOLDING_AND_ACTIVE.

This is a hack (adding sleep between the 2 commands). The actual fix is
expected to be more invasive and will touch stable code so avoiding that.
This code may be refactored in N so making minimal change for now.

Bug: 10680506
Change-Id: I0b106e082d357e1f464413d96e7cddd56dc53cc7