netrom: fix copying in user data in nr_setsockopt

This code used to copy in an unsigned long worth of data before
the sockptr_t conversion, so restore that.

Fixes: a7b75c5a

 ("net: pass a sockptr_t into ->setsockopt")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: David S. Miller <davem@davemloft.net>