rtnl_wilddump_request: fix alignment issue for embedded platforms

Platforms have different alignment requirements which need to be
fulfilled by the compiler. If the structure elements are already
4 byte (NLMGS_ALIGNTO) aligned by the compiler adding an explicit
padding element (align_rta) is not allowed.
Use __attribute__ ((aligned (NLMSG_ALIGNTO))) in order to achieve
the required alignment.
Experienced on ARM (xscale) with symptom
  netlink: 12 bytes leftover after parsing attributes

Tested on:
  ARM      (32bit Big Endian)
  PowerPC  (32bit Big Endian)
  x86_64   (64bit Little Endian)
Each with different aligment requirments.
Signed-off-by: Lutz Jaenicke <ljaenicke@innominate.com>

lib/libnetlink.c

@@ -94,8 +94,8 @@ int rtnl_wilddump_request(struct rtnl_handle *rth, int family, int type)
 	struct {
 		struct nlmsghdr nlh;
 		struct rtgenmsg g;
-		__u16 align_rta;	/* attribute has to be 32bit aligned */
-		struct rtattr ext_req;
+		/* attribute has to be NLMSG aligned */
+		struct rtattr ext_req __attribute__ ((aligned(NLMSG_ALIGNTO)));
 		__u32 ext_filter_mask;
 	} req;