Add a configuration variable "enable-timestamps"

Disabling the piggyback of timestamps can be useful if the per-message
overhead is not desirable, or for troubleshooting compatibility issues
(there should be none, but who knows).

babeld.man

@@ -330,6 +330,17 @@ interface; since Babel uses triggered updates and doesn't count to
 infinity, this can be set to a fairly large value, unless significant
 packet loss is expected.  The default is four times the hello interval.
 .TP
+.BR enable\-timestamps " {" true | false }
+This specifies whether we should send timestamps with each Hello and
+IHU message, in order to compute RTTs.  The overhead is about 8 bytes
+per message.  When set to
+.BR false ,
+the behaviour on this interface is identical to a non-RTT-aware
+babeld.  Namely, we are unable to compute RTTs, and our neighbours on
+this interface are also unable to compute RTTs to us.  The default is
+.B true
+for all interfaces.
+.TP
 .BI rtt\-exponential\-decay " decay"
 This specifies the decay factor for the exponential moving average of
 RTT samples, in units of 1/256.  Must be between 1 and 256, inclusive.

configuration.c

@@ -464,6 +464,12 @@ parse_anonymous_ifconf(int c, gnc_t gnc, void *closure,
             if((if_conf->channel < 1 || if_conf->channel > 255) &&
                if_conf->channel != IF_CHANNEL_NONINTERFERING)
                 goto error;
+        } else if(strcmp(token, "enable-timestamps") == 0) {
+            int v;
+            c = getbool(c, &v, gnc, closure);
+            if(c < -1)
+                goto error;
+            if_conf->enable_timestamps = v;
         } else if(strcmp(token, "rtt-exponential-decay") == 0) {
             int decay;
             c = getint(c, &decay, gnc, closure);