confd: Avoid needless Ethernet flow-control reconfigurations

Unless some configuration has changed that affects flow-control (only
auto-neg for now, until we allow actual configuration of flow-control
itself), do not issue any commands that might trigger a link down/up
cycle.

Additionally, make sure that we always configure it on boot, as the
driver defaults might not necessarily line up with our defaults.

src/confd/src/dagger.c

@@ -127,6 +127,10 @@ int dagger_should_skip_current(struct dagger *d, const char *ifname)
 	return fexistf("%s/%d/skip/%s", d->path, d->current, ifname);
 }
 
+int dagger_is_bootstrap(struct dagger *d)
+{
+	return d->next == 0;
+}
 
 int dagger_claim(struct dagger *d, const char *path)
 {

src/confd/src/dagger.h

@@ -30,6 +30,7 @@ int dagger_evolve_or_abandon(struct dagger *d);
 void dagger_skip_iface(struct dagger *d, const char *ifname);
 int dagger_should_skip(struct dagger *d, const char *ifname);
 int dagger_should_skip_current(struct dagger *d, const char *ifname);
+int dagger_is_bootstrap(struct dagger *d);
 
 int dagger_claim(struct dagger *d, const char *path);
 

src/confd/src/ietf-interfaces.c

@@ -775,12 +775,18 @@ static int netdag_gen_ethtool(struct dagger *net, struct lyd_node *cif, struct l
 	if (strcmp(type, "infix-if-type:ethernet"))
 		return 0;
 
-	/* XXX: add configurable flow-control support <<here>> */
-	err = netdag_gen_ethtool_flow_control(net, cif);
-	if (err)
-		return err;
+	if (!eth)
+		return 0;
 
-	if (lydx_get_descendant(lyd_child(eth), "auto-negotiation", "enable", NULL) ||
+	if (dagger_is_bootstrap(net) ||
+	    lydx_get_descendant(lyd_child(eth), "auto-negotiation", "enable", NULL)) {
+		err = netdag_gen_ethtool_flow_control(net, cif);
+		if (err)
+			return err;
+	}
+
+	if (dagger_is_bootstrap(net) ||
+	    lydx_get_descendant(lyd_child(eth), "auto-negotiation", "enable", NULL) ||
 	    lydx_get_child(eth, "speed") ||
 	    lydx_get_child(eth, "duplex")) {
 		err = netdag_gen_ethtool_autoneg(net, cif);