Core/Units: Second part of SMSG_MOVE_SET_COLLISION_HGT implementation: compute proper collision height according to client formulae and send this to the client when mounting up.

src/server/game/Entities/Unit/Unit.cpp

@@ -11934,6 +11934,12 @@ void Unit::Mount(uint32 mount, uint32 VehicleId, uint32 creatureEntry)
             else
                 player->UnsummonPetTemporaryIfAny();
         }
+
+        WorldPacket data(SMSG_MOVE_SET_COLLISION_HGT, GetPackGUID().size() + 4 + 4);
+        data.append(GetPackGUID());
+        data << uint32(sWorld->GetGameTime());   // Packet counter
+        data << player->GetCollisionHeight(true);
+        player->GetSession()->SendPacket(&data);
     }
 
     RemoveAurasWithInterruptFlags(AURA_INTERRUPT_FLAG_MOUNT);
@@ -11952,7 +11958,7 @@ void Unit::Unmount()
         WorldPacket data(SMSG_MOVE_SET_COLLISION_HGT, GetPackGUID().size() + 4 + 4);
         data.append(GetPackGUID());
         data << uint32(sWorld->GetGameTime());   // Packet counter
-        data << thisPlayer->GetCollisionHeight();
+        data << thisPlayer->GetCollisionHeight(false);
         thisPlayer->GetSession()->SendPacket(&data);
     }