Sockets: replace macroses concatenation with single one for netlink requests

NLM_F_DUMP is already defined as (NLM_F_ROOT|NLM_F_MATCH)

Signed-off-by: Stanislav Kinsbursky <skinsbursky@parallels.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>