commit <47595e32> ("<MAINTAINERS: Mark some staging directories>")
indicated the ipx network layer as obsolete in Jan 2018,
updated in the MAINTAINERS file

now, after being exposed for 3 years to refactoring,
so to delete the ipx net layer related code for good.

Signed-off-by: Cai Huoqing <caihuoqing@baidu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>