nl80211: remove unnecessary genlmsg_cancel() calls

If we free the message immediately, there's no reason to
trim it back to the previous size.

Done with spatch:

@@
identifier msg, hdr;
@@
-if (hdr)
-  genlmsg_cancel(msg, hdr);
... when != msg;
 nlmsg_free(msg);

@@
identifier msg, hdr;
@@
-genlmsg_cancel(msg, hdr);
... when != msg;
 nlmsg_free(msg);

Signed-off-by: Johannes Berg <johannes.berg@intel.com>