DHCP6: Improve logging when changing IA type

Changing from PD to IA or IA to PD can result in a diagnostic
when there is no address to confirm AND we haven't loaded
a lease.
This improves the check and no more Success errors should
be reported.

src/dhcp6.c

@@ -2589,21 +2589,17 @@ dhcp6_validatelease(struct interface *ifp,
 	}
 	state->has_no_binding = false;
 	nia = dhcp6_findia(ifp, m, len, sfrom, acquired);
-	if (nia == 0) {
-		if (state->state != DH6S_CONFIRM && ok_errno != 0) {
-			logerrx("%s: no useable IA found in lease", ifp->name);
-			return -1;
-		}
-
-		/* We are confirming and have an OK,
-		 * so look for ia's in our old lease.
-		 * IA's must have existed here otherwise we would
-		 * have rejected it earlier. */
-		assert(state->new != NULL && state->new_len != 0);
+	if (nia == 0 && state->state == DH6S_CONFIRM && ok_errno == 0 &&
+	    state->new && state->new_len)
+	{
 		state->has_no_binding = false;
 		nia = dhcp6_findia(ifp, state->new, state->new_len,
 		    sfrom, acquired);
 	}
+	if (nia == 0) {
+		logerrx("%s: no useable IA found in lease", ifp->name);
+		return -1;
+	}
 	return nia;
 }
 
@@ -2657,8 +2653,10 @@ dhcp6_readlease(struct interface *ifp, int validate)
 	/* Check to see if the lease is still valid */
 	fd = dhcp6_validatelease(ifp, &buf.dhcp6, (size_t)bytes, NULL,
 	    &state->acquired);
-	if (fd == -1)
+	if (fd == -1) {
+		bytes = 0; /* We have already reported the error */
 		goto ex;
+	}
 
 	if (state->expire != ND6_INFINITE_LIFETIME &&
 	    (time_t)state->expire < now - mtime &&