config: disable BPFILTER_UMH on non-x86 architectures (bsc#1127188)
    
    CONFIG_BPFILTER_UMH depends on ability to compile and link a userspace
    binary so that it currently doesn't work in our kbuild check setups using
    a cross compiler. Disable the option on architectures where cross compiler
    is used (i.e. all except x86_64 and i386).