CONFIG_MACH_NSLU2 is not available for the selected architecture x86.
Result is shown for architecture arm

NSLU2

modulename: nslu2-pci.ko

and/or

nslu2-setup.ko

configname: CONFIG_MACH_NSLU2

Linux Kernel Configuration
└─>Intel IXP4xx Implementation Options
└─>NSLU2
In linux kernel since version 2.6.15 (release Date: 2006-01-02)
Say 'Y' here if you want your kernel to support Linksys's
NSLU2 NAS device. For more information on this platform,
see http://www.nslu2-linux.org
source code:
selects
CONFIG_PCI
CONFIG_FORCE_PCI