net: put_cmsg_compat + SO_TIMESTAMP[NS]: use same name for value as caller

In __sock_recv_timestamp() the additional SCM_TIMESTAMP[NS] is used. This
has the same value as SO_TIMESTAMP[NS], so this is a purely cosmetic change.

Signed-off-by: Patrick Ohly <patrick.ohly@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>