r8169: napi config

Don't call napi_disable if not configured and make sure that any
misuse of napi_xxx in future fails with a compile error.

Signed-off-by: Stephen Hemminger <shemminger@linux-foundation.org>
Signed-off-by: Francois Romieu <romieu@fr.zoreil.com>
Cc: Edward Hsu <edward_hsu@realtek.com.tw>