ConnectivityService: update network settings when RAT changes

For radio subtype changes (GPRS/EDGE/UMTS/HSPA/etc on GSM), refresh
the network settings.
This causes the values from net.buffersize.<newtech> to be applied in
cases where a connectivity tech change does not imply an actual
reconnection, and applies the proper buffersizes (as configured) for
the new technology type

Change-Id: I7834d5cab5a7c9cfbebdcce81820238579d45177