selftests/drivers/net: Support ipv6 for napi_id test

Add support for IPv6 environment for napi_id test.

Test Plan:

    ./run_kselftest.sh -t drivers/net:napi_id.py
    TAP version 13
    1..1
    # timeout set to 45
    # selftests: drivers/net: napi_id.py
    # TAP version 13
    # 1..1
    # ok 1 napi_id.test_napi_id
    # # Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0
    ok 1 selftests: drivers/net: napi_id.py

Signed-off-by: Tianyi Cui <1997cui@gmail.com>
Link: https://patch.msgid.link/20250717011913.1248816-1-1997cui@gmail.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>