net: rtl8169: Build warning fixes for 64-bit

Turn ioaddr into an unsigned long rather than a sized 32-bit variable.
While at it, fix a couple of pointer to integer cast size mismatch
warnings by casting through unsigned long going from pointers to
integers and vice versa.

Cc: Joe Hershberger <joe.hershberger@gmail.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>