net: remove unnecessary genlmsg_cancel() calls

the message be freed immediately, no need to trim it
back to the previous size.

Inspired by commit 7a9b3ec1 ("nl80211: remove unnecessary genlmsg_cancel() calls")

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>