Getting interface params in ClearingIpAddressState#enter.

In case of wifi might stop IpClient and then restart prov immediately
to avoid wifi disconnection especially when roaming happens, this
might cause getting interface params with incorrect interface mtu when
starting provisioning again before interface mtu hasn't been restored.

Moving getting interface params to ClearingIpAddressState#enter ensures
that interface parameters are fetched on the handler thread so they are
properly ordered with other events, such as restoring the interface MTU
on teardown.

Bug: 152169857
Test: atest NetworkStackIntegrationTests NetworkStackTests

Change-Id: I5e98d59488f24bcfdb673fcb2877e27d81432a13