ynl: samples: add tc filter example

ynl: samples: add tc filter example

Add a sample tool demonstrating how to add, dump, and delete a
flower filter with two VLAN push actions. The example can be
invoked as:

  # samples/tc-filter-add p2

    flower pref 1 proto: 0x8100
    flower:
      vlan_id: 100
      vlan_prio: 5
      num_of_vlans: 3
    action order: 1 vlan push id 200 protocol 0x8100 priority 0
    action order: 2 vlan push id 300 protocol 0x8100 priority 0

This verifies correct handling of tc action attributes for multiple
VLAN push actions. The tc action indexed arrays start from index 1,
and the index defines the action order. This behavior differs from
the YNL specification, which expects arrays to be zero-based. To
accommodate this, the example adds a dummy action at index 0, which
is ignored by the kernel.

Signed-off-by: Zahari Doychev <zahari.doychev@linux.com>
Link: https://patch.msgid.link/20251119203618.263780-2-zahari.doychev@linux.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>