Fixed a race condition when attaching network request

When attaching the network request to the data network,
the network request might have been removed by the
clients. Need to check if the request is present or not
when we are attaching it.

Fix: 223468685
Test: atest DataNetworkControllerTest
Change-Id: I87a37849caefb62c7da5004a1f51ad6d81b2d820