Add support Controller Area Network

t's not a big problem, but it makes a better show in 'ip link show' on
CAN interfaces :-)

I also moved __PF(CAN,can) in ll_proto.c to the same position where it
can be found in if_ether.h .

The only thing i did not know if the __PF(CAN,can) in ll_types.c needs
to be put in #ifdef ARPHDR_CAN like __PF(HWX25,hwx25) is or not. You
definitely know that better than me.
diff --git a/ip/ipaddress.c b/ip/ipaddress.c
index b055b68..267ecb3 100644
--- a/ip/ipaddress.c
+++ b/ip/ipaddress.c
@@ -109,6 +109,7 @@
 	_PF(UP);
 	_PF(LOWER_UP);
 	_PF(DORMANT);
+	_PF(ECHO);
 #undef _PF
         if (flags)
 		fprintf(fp, "%x", flags);