Debian patch used original code for 32-bit and sizeof(struct ifreq) for 64-bit builds,
but the latter is exactly what Linux kernel does everywhere.
diff -urNad src/get_myipaddr.c trunk/src/get_myipaddr.c
--- src/get_myipaddr.c	2009-09-03 13:10:32.000000000 +0200
+++ src/get_myipaddr.c	2009-09-03 13:15:39.671451172 +0200
@@ -118,7 +118,7 @@
 #endif /* not STRUCT_SOCKADDR_HAS_SA_LEN */
 
 		/* increment ptr to next interface for next time through the loop */
-		ptr += sizeof(ifr->ifr_name) + len;
+		ptr += sizeof(struct ifreq);
 
 		if (strcmp(ifname, ifr->ifr_name) != 0 )  /* is this the interface we're looking for? */
 			continue;