Adding 1s time gap between slot1 & slot2 setDataThrottling tests

  Modem has restriction that it can not process back-to-back thermal actions.
  For DSDS device, after slot-1 test finished, a 1s delay is needed before start slot-2 test.

Bug: 187968151
Test: atest VtsHalRadioV1_6TargetTest -- --test-arg com.android.tradefed.testtype.GTest:native-test-flag:"--gtest_filter=*setDataThrottling*"
Change-Id: I052d0d9c7c0ccc86a7590204679295268973c6cf