Some paths of a device cant be requested more than once

Requesting a path like, e.g. /system multiple times throws errors

Description

While requesting config data from a gnmi/openconfig target, paths with values that can change like, e.g. /system (contains memory information - which can change) results in an error:

{"level":"error","msg":"destination value was set, but was not equal to source value when merging ptr field, (-src, +dst):\n  uint64(\n- \t17760522240,\n+ \t17762693120,\n  )\n","time":"2021-11-17T18:08:30+01:00"}

Since the values are different an error is thrown from within the ygot.MergeStructInto

Expected Behavior

values should be updated and the corresponding ygot.GoStruct of Device should contain the up to date data.

Actual Behavior

the merge fails and an error is thrown

Possible Fix

allow the merge to overwrite values. this can probably be done by

Steps to Reproduce

1. request a path like /system -> success
2. request it once more -> error