sys/linux/socket_netlink_generic_devlink: use template type for netlink msg
sys/linux/socket_netlink_generic_devlink: use template type for netlink msg

Add template type for netlink msg with CMD and POLICY as
arguments, it can be used for all sendmsg calls in this file.

Refactor the existing code.

Signed-off-by: Amit Cohen <14d0af1387c96a35b2eae32162a78d32c55d88c4@mellanox.com>

google/syzkaller,xairy/syzkaller,google/syzkaller,xairy/syzkaller,xairy/syzkaller,xairy/syzkaller,xairy/syzkaller,google/syzkaller,google/syzkaller,google/syzkaller,xairy/syzkaller,google/syzkaller,xairy/syzkaller,google/syzkaller