Convert netdev.c to produce KTAP output with 3 tests:
- dev_dump: dump all netdev devices, skip if empty
- dev_get: query first device from dump by ifindex
- ntf_check: subscribe to "mgmt", create a veth via rt-link,
  verify netdev notification is received, then delete the veth

Remove stdin/scanf-based UI. Add rt-link dependency for the veth
notification test.

  TAP version 13
  1..3
  # Starting 3 tests from 1 test cases.
  #  RUN           netdev.dump ...
  #       lo[1]	xdp-features (0): xdp-rx-metadata-features (0): xsk-fea...
  #     sit0[2]	xdp-features (0): xdp-rx-metadata-features (0): xsk-fea...
  #            OK  netdev.dump
  ok 1 netdev.dump
  #  RUN           netdev.get ...
  #       lo[1]	xdp-features (0): xdp-rx-metadata-features (0): xsk-fea...
  #            OK  netdev.get
  ok 2 netdev.get
  #  RUN           netdev.ntf_check ...
  #    veth0[7]	xdp-features (0): xdp-rx-metadata-features (7): timesta...
  #            OK  netdev.ntf_check
  ok 3 netdev.ntf_check
  # PASSED: 3 / 3 tests passed.
  # Totals: pass:3 fail:0 xfail:0 xpass:0 skip:0 error:0

Reviewed-by: Donald Hunter <donald.hunter@gmail.com>
Tested-by: Donald Hunter <donald.hunter@gmail.com>
Link: https://patch.msgid.link/20260307033630.1396085-3-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

The "samples" were always poor man's tests (used to manually
confirm that C YNL works).

Move all C sample programs from tools/net/ynl/samples/ to
tools/net/ynl/tests/, "merge" the Makefiles. The subsequent
changes will convert each sample into a proper KTAP selftests.

Since these are now tests rather than samples - default to
enabling asan. After all we're testing user space code here.

Sort the gitignore while at it, the page-pool entry was a leftover
so delete it.

Reviewed-by: Donald Hunter <donald.hunter@gmail.com>
Tested-by: Donald Hunter <donald.hunter@gmail.com>
Link: https://patch.msgid.link/20260307033630.1396085-2-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>