Add test to coverage dynamic enable/disable watch for RAT type changes

Save the current netstats_combine_subtype_enabled setting.
Then change the value to true/false and verify the data is
expected.
Restore netstats_combine_subtype_enabled to original setting.

Bug: 154080515
Test: atest CtsStatsdHostTestCases:UidAtomTests#testDataUsageBytesTransfer
Change-Id: Iddc297971125cbce7dde99a1ec2d0718828b7494