fix problem caused by rtnl_send checks

Some usages of rtnl_send could cause errors (ie flush requests)
others do a listen afterwards.

Signed-off-by: Stephen Hemminger <stephen.hemminger@vyatta.com>
diff --git a/ip/iproute.c b/ip/iproute.c
index 685cb85..2a8f3f8 100644
--- a/ip/iproute.c
+++ b/ip/iproute.c
@@ -112,7 +112,7 @@
 
 static int flush_update(void)
 {
-	if (rtnl_send(&rth, filter.flushb, filter.flushp) < 0) {
+	if (rtnl_send_check(&rth, filter.flushb, filter.flushp) < 0) {
 		perror("Failed to send flush request");
 		return -1;
 	}