PPP: fix constness in PPP related files (GCC -Wcast-qual)

Signed-off-by: Dirk Ziegelmeier <dirk@ziegelmeier.net>

src/include/netif/ppp/chap-new.h

@@ -140,7 +140,7 @@ struct chap_digest_type {
 #endif /* PPP_SERVER */
 	void (*make_response)(ppp_pcb *pcb, unsigned char *response, int id, const char *our_name,
 		const unsigned char *challenge, const char *secret, int secret_len,
-		const unsigned char *priv);
+		unsigned char *priv);
 	int (*check_success)(ppp_pcb *pcb, unsigned char *pkt, int len, unsigned char *priv);
 	void (*handle_failure)(ppp_pcb *pcb, unsigned char *pkt, int len);
 };

src/include/netif/ppp/fsm.h

@@ -168,7 +168,7 @@ void fsm_open(fsm *f);
 void fsm_close(fsm *f, const char *reason);
 void fsm_input(fsm *f, u_char *inpacket, int l);
 void fsm_protreject(fsm *f);
-void fsm_sdata(fsm *f, u_char code, u_char id, u_char *data, int datalen);
+void fsm_sdata(fsm *f, u_char code, u_char id, const u_char *data, int datalen);
 
 
 #endif /* FSM_H */

src/include/netif/ppp/polarssl/des.h

@@ -80,7 +80,7 @@ void des_setkey_dec( des_context *ctx, unsigned char key[8] );
  * \param output   64-bit output block
  */
 void des_crypt_ecb( des_context *ctx,
-                    unsigned char input[8],
+                    const unsigned char input[8],
                     unsigned char output[8] );
 
 #ifdef __cplusplus

src/include/netif/ppp/polarssl/md4.h

@@ -68,7 +68,7 @@ void md4_starts( md4_context *ctx );
  * \param input    buffer holding the  data
  * \param ilen     length of the input data
  */
-void md4_update( md4_context *ctx, unsigned char *input, int ilen );
+void md4_update( md4_context *ctx, const unsigned char *input, int ilen );
 
 /**
  * \brief          MD4 final digest

src/include/netif/ppp/polarssl/md5.h

@@ -68,7 +68,7 @@ void md5_starts( md5_context *ctx );
  * \param input    buffer holding the  data
  * \param ilen     length of the input data
  */
-void md5_update( md5_context *ctx, unsigned char *input, int ilen );
+void md5_update( md5_context *ctx, const unsigned char *input, int ilen );
 
 /**
  * \brief          MD5 final digest

src/include/netif/ppp/polarssl/sha1.h

@@ -68,7 +68,7 @@ void sha1_starts( sha1_context *ctx );
  * \param input    buffer holding the  data
  * \param ilen     length of the input data
  */
-void sha1_update( sha1_context *ctx, unsigned char *input, int ilen );
+void sha1_update( sha1_context *ctx, const unsigned char *input, int ilen );
 
 /**
  * \brief          SHA-1 final digest