Fix some missing void * and const in existing APIs.

Several changes here that should have been in commit 7babe66a8 but I
missed them.

portfwd.c

@@ -605,7 +605,7 @@ void pfd_override_throttle(struct PortForwarding *pf, int enable)
 /*
  * Called to send data down the raw connection.
  */
-int pfd_send(struct PortForwarding *pf, char *data, int len)
+int pfd_send(struct PortForwarding *pf, const void *data, int len)
 {
     if (pf == NULL)
 	return 0;

ssh.c

@@ -5890,7 +5890,7 @@ static void ssh1_msg_channel_close(Ssh ssh, struct Packet *pktin)
 /*
  * Handle incoming data on an SSH-1 or SSH-2 agent-forwarding channel.
  */
-static int ssh_agent_channel_data(struct ssh_channel *c, char *data,
+static int ssh_agent_channel_data(struct ssh_channel *c, const void *data,
 				  int length)
 {
     bufchain_add(&c->u.a.inbuffer, data, length);
@@ -5908,7 +5908,7 @@ static int ssh_agent_channel_data(struct ssh_channel *c, char *data,
 }
 
 static int ssh_channel_data(struct ssh_channel *c, int is_stderr,
-			    char *data,  int length)
+			    const void *data, int length)
 {
     switch (c->type) {
       case CHAN_MAINSESSION:

ssh.h

@@ -226,7 +226,7 @@ struct ec_key *ssh_ecdhkex_newkey(const struct ssh_kex *kex);
 void ssh_ecdhkex_freekey(struct ec_key *key);
 void ssh_ecdhkex_getpublic(struct ec_key *key, BinarySink *bs);
 Bignum ssh_ecdhkex_getkey(struct ec_key *key,
-                          char *remoteKey, int remoteKeyLen);
+                          const void *remoteKey, int remoteKeyLen);
 
 /*
  * Helper function for k generation in DSA, reused in ECDSA
@@ -542,7 +542,7 @@ void ssh_send_port_open(void *channel, const char *hostname, int port,
 extern char *pfd_connect(struct PortForwarding **pf, char *hostname, int port,
                          void *c, Conf *conf, int addressfamily);
 extern void pfd_close(struct PortForwarding *);
-extern int pfd_send(struct PortForwarding *, char *data, int len);
+extern int pfd_send(struct PortForwarding *, const void *data, int len);
 extern void pfd_send_eof(struct PortForwarding *);
 extern void pfd_confirm(struct PortForwarding *);
 extern void pfd_unthrottle(struct PortForwarding *);
@@ -622,7 +622,7 @@ void x11_free_fake_auth(struct X11FakeAuth *auth);
 struct X11Connection;                  /* opaque outside x11fwd.c */
 struct X11Connection *x11_init(tree234 *authtree, void *, const char *, int);
 extern void x11_close(struct X11Connection *);
-extern int x11_send(struct X11Connection *, char *, int);
+extern int x11_send(struct X11Connection *, const void *, int);
 extern void x11_send_eof(struct X11Connection *s);
 extern void x11_unthrottle(struct X11Connection *s);
 extern void x11_override_throttle(struct X11Connection *s, int enable);

sshecc.c

@@ -2689,7 +2689,8 @@ void ssh_ecdhkex_getpublic(struct ec_key *ec, BinarySink *bs)
     }
 }
 
-Bignum ssh_ecdhkex_getkey(struct ec_key *ec, char *remoteKey, int remoteKeyLen)
+Bignum ssh_ecdhkex_getkey(struct ec_key *ec,
+                          const void *remoteKey, int remoteKeyLen)
 {
     struct ec_point remote;
     Bignum ret;
@@ -2708,7 +2709,8 @@ Bignum ssh_ecdhkex_getkey(struct ec_key *ec, char *remoteKey, int remoteKeyLen)
 
         remote.curve = ec->publicKey.curve;
         remote.infinity = 0;
-        remote.x = bignum_from_bytes_le((unsigned char*)remoteKey, remoteKeyLen);
+        remote.x = bignum_from_bytes_le((const unsigned char *)remoteKey,
+                                        remoteKeyLen);
         remote.y = NULL;
         remote.z = NULL;
     }

x11fwd.c

@@ -800,8 +800,10 @@ static int x11_parse_ip(const char *addr_string, unsigned long *ip)
 /*
  * Called to send data down the raw connection.
  */
-int x11_send(struct X11Connection *xconn, char *data, int len)
+int x11_send(struct X11Connection *xconn, const void *vdata, int len)
 {
+    const char *data = (const char *)vdata;
+
     if (!xconn)
 	return 0;