Pull up to ETHER_HDR_LEN before passing an mbuf to ether_input().

The bug was found by running ng_dummy(4) node configured with a
delay, in front of the ng_eiface(4) node.

sys/netgraph/ng_eiface.c

@@ -613,6 +613,12 @@ ng_eiface_rcvdata(hook_p hook, item_p item)
 		return (ENETDOWN);
 	}
 
+	if (m->m_len < ETHER_HDR_LEN) {
+		m = m_pullup(m, ETHER_HDR_LEN);
+		if (m == NULL)
+			return (EINVAL);
+	}
+
 	/* Note receiving interface */
 	m->m_pkthdr.rcvif = ifp;