Add missing "goto set_head" for SO_IPX_CHECKSUM; otherwise we fall through

to the SO_HEADERS_ON_OUTPUT case and set that instead.

MFC after:	1 week
Found with:	Coverity Prevent(tm)
Coverity ID:	3988

sys/netipx/ipx_usrreq.c

@@ -412,6 +412,7 @@ ipx_ctloutput(struct socket *so, struct sockopt *sopt)
 
 		case SO_IPX_CHECKSUM:
 			mask = IPXP_CHECKSUM;
+			goto set_head;
 
 		case SO_HEADERS_ON_OUTPUT:
 			mask = IPXP_RAWOUT;