CVE-2023-1667:dh: Expose the callback cleanup functions

These will be helpful when we already sent the first key exchange packet, but we
found out that our guess was wrong and we need to initiate different key
exchange method with different callbacks.

Signed-off-by: Jakub Jelen <jjelen@redhat.com>
Reviewed-by: Norbert Pocs <npocs@redhat.com>
Reviewed-by: Andreas Schneider <asn@cryptomilk.org>

include/libssh/curve25519.h

@@ -52,6 +52,7 @@ typedef unsigned char ssh_curve25519_privkey[CURVE25519_PRIVKEY_SIZE];
 
 
 int ssh_client_curve25519_init(ssh_session session);
+void ssh_client_curve25519_remove_callbacks(ssh_session session);
 
 #ifdef WITH_SERVER
 void ssh_server_curve25519_init(ssh_session session);

include/libssh/dh-gex.h

@@ -28,6 +28,7 @@ extern "C" {
 #endif
 
 int ssh_client_dhgex_init(ssh_session session);
+void ssh_client_dhgex_remove_callbacks(ssh_session session);
 
 #ifdef WITH_SERVER
 void ssh_server_dhgex_init(ssh_session session);

include/libssh/dh.h

@@ -79,6 +79,7 @@ int ssh_dh_get_next_server_publickey_blob(ssh_session session,
                                           ssh_string *pubkey_blob);
 
 int ssh_client_dh_init(ssh_session session);
+void ssh_client_dh_remove_callbacks(ssh_session session);
 #ifdef WITH_SERVER
 void ssh_server_dh_init(ssh_session session);
 #endif /* WITH_SERVER */

include/libssh/ecdh.h

@@ -49,6 +49,7 @@ extern "C" {
 extern struct ssh_packet_callbacks_struct ssh_ecdh_client_callbacks;
 /* Backend-specific functions.  */
 int ssh_client_ecdh_init(ssh_session session);
+void ssh_client_ecdh_remove_callbacks(ssh_session session);
 int ecdh_build_k(ssh_session session);
 
 #ifdef WITH_SERVER