CONFIG_MACH_NET2BIG is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

LaCie 2Big Network

modulename: net2big-setup.ko

configname: CONFIG_MACH_NET2BIG

Linux Kernel Configuration
└─>Orion Implementations
└─>LaCie 2Big Network
In linux kernel since version 2.6.32 (release Date: 2009-12-02)  
Say 'Y' here if you want your kernel to support the
LaCie 2Big Network NAS.

source code:
arch/arm/mach-orion5x/net2big-setup.c

depends
CONFIG_ARCH_ORION5X |
| CONFIG_ATAGS