Add export policy test cases to link bandwidth test (openconfig#3522)

* Add export policy test cases to link bandwidth test

* update not_match_100_set_linkbw_1M policy to add statement to remove any LBw before adding the new LBw

* added both kbps and KBps comparison

* removed old import and export policies

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Co-authored-by: rszarecki <[email protected]>