Don't include a NUL at the end of our CHAP SUCCESS packet.

When encryption (MPPE) is enabled, WindowsME and Windows98 both
fail because of the extra byte, suggesting that they autheticated
successfully in their log and then dropping the connection, telling
the user that the peer doesn't support compatible encryption
options.

MFC after: 1 week

usr.sbin/ppp/chap.c

@@ -549,7 +549,7 @@ chap_Success(struct authinfo *authp)
 #endif
     msg = "Welcome!!";
 
-  ChapOutput(authp->physical, CHAP_SUCCESS, authp->id, msg, strlen(msg) + 1,
+  ChapOutput(authp->physical, CHAP_SUCCESS, authp->id, msg, strlen(msg),
              NULL);
 
   authp->physical->link.lcp.auth_ineed = 0;