staging: ipx: depends on NET

IPX depends on NET, so add that to the Kconfig file.

Fixes Kconfig warning and build errors:

warning: (IPX) selects LLC which has unmet direct dependencies (NET)
and 94 "undefined reference" build errors.

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>