net: Add framework to allow sending packets with customized CRC.

This is useful for testing RX handling of frames with bad
CRCs.

Requires driver support to actually put the packet on the
wire properly.

Signed-off-by: Ben Greear <greearb@candelatech.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

net/core/skbuff.c

@@ -592,6 +592,7 @@ static void __copy_skb_header(struct sk_buff *new, const struct sk_buff *old)
 	new->rxhash		= old->rxhash;
 	new->ooo_okay		= old->ooo_okay;
 	new->l4_rxhash		= old->l4_rxhash;
+	new->no_fcs		= old->no_fcs;
 #ifdef CONFIG_XFRM
 	new->sp			= secpath_get(old->sp);
 #endif

net/core/sock.c

@@ -799,6 +799,11 @@ set_rcvbuf:
 		else
 			ret = -EOPNOTSUPP;
 		break;
+
+	case SO_NOFCS:
+		sock_valbool_flag(sk, SOCK_NOFCS, valbool);
+		break;
+
 	default:
 		ret = -ENOPROTOOPT;
 		break;