Revert defer unlock in StayRTR AddVRPs

[BenCastricum]

vrplock needs to be unlocked before AddVRPsDiff() because AddVRPsDiff needs a full lock.

I added some debug logging found this deadlock

INFO[0000] new cache file: Updating sha256 hash -> da753c7804d6f386bf303fed6931853eaaca0771ba160ef7fdbebb17e899d78b
INFO[0001] New update (306189 uniques, 306189 total prefixes).
INFO[0001] RLocking vrplock in AddVRPs
INFO[0002] RLocking vrplock in AddVRPsDiff
INFO[0002] RUnlocked vrplock in AddVRPsDiff
INFO[0002] Locking vrplock in AddVRPsDiff
...

[ties]

This reverts 3726782 in AddVRPs. Looks good to me. Will ask @lspgn for a second opinion.

[ties]

And thanks for debugging this and your contribution!

[lspgn]

Good catch.
One pattern I've been seeing which could improve this code

func (s *Server) addVRPsDiff(diff []VRP) {
   [...]
}


func (s *Server) AddVRPsDiff(diff []VRP) {
	s.vrplock.RLock()
	s.addVRPsDiff(diff)
	s.vrplock.RUnlock()
}

And the internal functions would call s.addVRPsDiff(diff)