Adjust PermissionMonitor#startMonitoring in ConnectivityService

Let PermissionMonitor#startMonitoring() running in the beginning
of the ConnectivityService#systemReady() before
MultipathPolicyTracker.start(). Since mApps in PermissionMonitor
needs to be populated first to ensure that listening network
request which is sent by MultipathPolicyTracker won't be added
NET_CAPABILITY_FOREGROUND capability.

Bug: 135897744
Test: atest FrameworksNetTests
Change-Id: Ibef8e7b0017a77384630d34c9edc6c40875f773e