znet: fix build failure from i82593.h relocation

znet was including "wireless/i82593.h" (which is a bit wierd), and I
missed that when I relocated i82593.h to drivers/staging/wavelan.  Since
I don't have ISA turned-on in my normal .config, I didn't see the build
failures -- mea culpa!

Signed-off-by: John W. Linville <linville@tuxdriver.com>