ipacm: set upstream flag if downstream IP addr event come later

If IPA_ADDR_EVENT for downstream event comes after IPA_WAN_UP_TETHER
event, upstream flag is not getting set. So later even after
receiving downstream event UL rules will not be installed. Set
upstream flag after receiving IPA_WAN_UP_TETHER event

Change-Id: I96c23b0e2e8aea20b5cdbf67a7f4d0d50b75e6db