test_rtnetlink: Increase interations in WithSingleInterface

We were hitting test failures caused by

    EXPECT_EQ(true, isInterfaceAdded("igb5"));

at the end of the WithSingleInterface case. There appears to be a race
condition between the netlink handling and the timer expiry, so
increment the number of retries for test stability.

Change-Id: I6cd2e4e95ee4d183466c73fa8a36a5580f566227
Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
diff --git a/test/test_rtnetlink.cpp b/test/test_rtnetlink.cpp
index 71e5443..79d9547 100644
--- a/test/test_rtnetlink.cpp
+++ b/test/test_rtnetlink.cpp
@@ -122,7 +122,7 @@
     // Send the request
     send(smartSock(), nlMsg, nlMsg->nlmsg_len, 0);
 
-    int i = 2;
+    int i = 3;
     while (i--)
     {
         //wait for timer to expire