tools: ynl: convert ovs sample to selftest

tools: ynl: convert ovs sample to selftest

Convert ovs.c to produce KTAP output with kselftest_harness.
The single "crud" test creates a new OVS datapath, fetches it back
by name, then dumps all datapaths verifying the new one appears.

IIRC I added this test because ovs is a genetlink family but
has a family-specific fixed header.

  TAP version 13
  1..1
  # Starting 1 tests from 1 test cases.
  #  RUN           ovs.crud ...
  # get:
  # ynl-test(3): pid:0 cache:256
  # dump:
  # ynl-test(3): pid:0 cache:256
  #            OK  ovs.crud
  ok 1 ovs.crud
  # PASSED: 1 / 1 tests passed.
  # Totals: pass:1 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/20260307033630.1396085-4-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>