Re-adding an event to a kqueue modifies the parameters of the original event.
However, if the original knote had been disabled then it is not automatically
re-enabled.

Fix this by using EV_ADD to create an mevent and EV_ENABLE to enable it.

Adding a kevent for the first time implicitly enables it so existing callers
of mevent_add() don't need to change.

Reviewed by:	grehan

Index: mevent.c
===================================================================
--- mevent.c	(revision 265252)
+++ mevent.c	(working copy)
@@ -55,6 +55,7 @@
 #define MEV_ENABLE	1
 #define MEV_DISABLE	2
 #define MEV_DEL_PENDING	3
+#define	MEV_ADD		4
 
 extern char *vmname;
 
@@ -147,10 +148,11 @@
 	int ret;
 
 	switch (mevp->me_state) {
+	case MEV_ADD:
+		ret = EV_ADD;		/* implicitly enabled */
+		break;
 	case MEV_ENABLE:
-		ret = EV_ADD;
-		if (mevp->me_type == EVF_TIMER)
-			ret |= EV_ENABLE;
+		ret = EV_ENABLE;
 		break;
 	case MEV_DISABLE:
 		ret = EV_DISABLE;
@@ -158,6 +160,9 @@
 	case MEV_DEL_PENDING:
 		ret = EV_DELETE;
 		break;
+	default:
+		assert(0);
+		break;
 	}
 
 	return (ret);
@@ -284,7 +289,7 @@
 
 	LIST_INSERT_HEAD(&change_head, mevp, me_list);
 	mevp->me_cq = 1;
-	mevp->me_state = MEV_ENABLE;
+	mevp->me_state = MEV_ADD;
 	mevent_notify();
 
 exit: