Define API to get the link peer_id using peer_id and lmac_id.
This is required in Rx monitor path for stats updation as Rx
monitor provides MLD peer id, whereas stats updation is done
for link peer.
Change-Id: Ib1c9e2729ccaea2e28272b7d175b3ef7fba9fd7a
CRs-Fixed: 3133003