VTS: stop network scan once trigger network scan success

For some vendors do not supports independent radios, if
there is one manual search ongoing, another manual search
on other SIM is not supported. So sending stop network scan
request once trigger network scan completed to exclude this
modem limitation.

Bug: 135005200
Test: atest RadioHidlTest_v1_2#startNetworkScan

Change-Id: Iacfd59ac2ad4d44e763ee03697c1f8f57162ce38