tools: Fix memset(&p,0,sizeof(p)) idiom in several places.

gcc 4.8 identifies several places where code of the form memset(x, 0,
sizeof(x)); is used incorrectly, meaning that less memory is set to
zero than required.

Signed-off-by: Michael Young <m.a.young@durham.ac.uk>
Committed-by: Keir Fraser <keir@xen.org>
(cherry picked from commit d119301b58)

tools/python/xen/lowlevel/netlink/libnetlink.c

@@ -37,7 +37,7 @@ int rtnl_open_byproto(struct rtnl_handle *rth, unsigned subscriptions,
        int sndbuf = 32768;
        int rcvbuf = 32768;
 
-       memset(rth, 0, sizeof(rth));
+       memset(rth, 0, sizeof(*rth));
 
        rth->fd = socket(AF_NETLINK, SOCK_RAW, protocol);
        if (rth->fd < 0) {