Core/Player: Add a helper function in Player to get the number of grantable levels. For future use. Thanks Phazerz for helping me confirm this is the right value.

src/server/game/Entities/Player/Player.h

@@ -1936,6 +1936,7 @@ class Player : public Unit, public GridObject<Player>
         bool isHonorOrXPTarget(Unit* pVictim);
 
         bool GetsRecruitAFriendBonus(bool forXP);
+        uint8 GetGrantableLevels() { return GetByteValue(PLAYER_FIELD_BYTES, 1); }
 
         ReputationMgr&       GetReputationMgr()       { return m_reputationMgr; }
         ReputationMgr const& GetReputationMgr() const { return m_reputationMgr; }