[CCID]: Make ccid_hc_[rt]x_exit accept NULL arguments

Just like kfree, etc it will just not call the CCID exit
routines when the private data area is set to NULL.
Signed-off-by: NArnaldo Carvalho de Melo <acme@mandriva.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/dccp/ccid.h

@@ -97,13 +97,15 @@ static inline int ccid_hc_tx_init(struct ccid *ccid, struct sock *sk)
 
 static inline void ccid_hc_rx_exit(struct ccid *ccid, struct sock *sk)
 {
-	if (ccid->ccid_hc_rx_exit != NULL)
+	if (ccid->ccid_hc_rx_exit != NULL &&
+	    dccp_sk(sk)->dccps_hc_rx_ccid_private != NULL)
 		ccid->ccid_hc_rx_exit(sk);
 }
 
 static inline void ccid_hc_tx_exit(struct ccid *ccid, struct sock *sk)
 {
-	if (ccid->ccid_hc_tx_exit != NULL)
+	if (ccid->ccid_hc_tx_exit != NULL &&
+	    dccp_sk(sk)->dccps_hc_tx_ccid_private != NULL)
 		ccid->ccid_hc_tx_exit(sk);
 }