ssh_userauth_publickey_auto requires three arguments.

Addressing
client.c: In function ‘authenticate_pubkey’:
client.c:70:8: error: too few arguments to function ‘ssh_userauth_publickey_auto’
   rc = ssh_userauth_publickey_auto(session, NULL);
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from client.c:1:
/usr/include/libssh/libssh.h:745:16: note: declared here
 LIBSSH_API int ssh_userauth_publickey_auto(ssh_session session,
                ^~~~~~~~~~~~~~~~~~~~~~~~~~~

Signed-off-by: Jan Pazdziora <jpazdziora@redhat.com>
Reviewed-by: Andreas Schneider <asn@cryptomilk.org>

doc/authentication.dox

@@ -63,7 +63,7 @@ int authenticate_pubkey(ssh_session session)
 {
   int rc;
 
-  rc = ssh_userauth_publickey_auto(session, NULL);
+  rc = ssh_userauth_publickey_auto(session, NULL, NULL);
 
   if (rc == SSH_AUTH_ERROR)
   {