Move the oversize ethernet frame size check into DIAGNOSTIC,

as was proposed when it was originally added.  This allows
LRO to work on non-DIAGNOSTIC kernels without consuming
any mbuf flags.

Discussed with: sam

sys/net/if_ethersubr.c

@@ -542,6 +542,7 @@ ether_input(struct ifnet *ifp, struct mbuf *m)
 	}
 	eh = mtod(m, struct ether_header *);
 	etype = ntohs(eh->ether_type);
+#ifdef DIAGNOSTIC
 	if (m->m_pkthdr.len >
 	    ETHER_MAX_FRAME(ifp, etype, m->m_flags & M_HASFCS)) {
 		if_printf(ifp, "discard oversize frame "
@@ -553,6 +554,7 @@ ether_input(struct ifnet *ifp, struct mbuf *m)
 		m_freem(m);
 		return;
 	}
+#endif
 	if (m->m_pkthdr.rcvif == NULL) {
 		if_printf(ifp, "discard frame w/o interface pointer\n");
 		ifp->if_ierrors++;