Rename EXTRA_NETWORK ConnectivityManager constants.

Per b/18414703:

    s/\<EXTRA_NETWORK_REQUEST_NETWORK\>/EXTRA_NETWORK/g
    s/\<EXTRA_NETWORK_REQUEST_NETWORK_REQUEST\>/EXTRA_NETWORK_REQUEST/g

Additionally, associated string values updated to:

    android.net.extra.NETWORK
    android.net.extra.NETWORK_REQUEST

Bug: 18414703
Change-Id: I7aeed2161829742affc666e835a97ce2c28356fe