docs: update 2n-clx job_specs for report_iterative

Changes in vpp-2n-clx.md:
- all nfv_density moved to separate file vpp-2n-clx-nfv-density.md
- removed intel-x710: dot1q
- removed drv_vfio_pci: vts, dot1q

- Rebased on https://gerrit.fd.io/r/c/csit/+/27495
- *.md files moved to docs/job_specs/report_iterative/2n-clx/ and
  renamed

Change-Id: I639abe794bde511d27cefa50db2860945dcc0050
Signed-off-by: Maciek Konstantynowicz <mkonstan@cisco.com>