netmap_poll should check if interface is up

[jcaplan]

running pkt-gen -i ix -f tx on ix or ixl interfaces, there is a period before the hardware is ready where it looks like pkt-gen is writing 30Gb/s on a 10Gb line. Eventually once the link state changes to up then the throughput comes down to something sane and packets actually start getting sent. I'm not sure poll should be returning ready in these instances so something like:

diff --git a/sys/dev/netmap/netmap.c b/sys/dev/netmap/netmap.c
index e5f6e1f1..e86ffcdd 100644
--- a/sys/dev/netmap/netmap.c
+++ b/sys/dev/netmap/netmap.c
@@ -3711,6 +3711,10 @@ netmap_poll(struct netmap_priv_d *priv, int events, NM_SELRECORD_T *sr)
                return POLLERR;
        }
 
+       if (na->ifp != NULL &&  na->ifp->if_link_state != LINK_STATE_UP) {
+               return 0;
+       }
+
        if (netmap_debug & NM_DEBUG_ON)
                nm_prinf("device %s events 0x%x", na->name, events);
        want_tx = events & (POLLOUT | POLLWRNORM);