filetable: Use relaxed stores to initialize
filetable: Use relaxed stores to initialize

Previously, there was an mfence in the loops that initialized and copied
filetable.  This improves forktest 80 40 by 20%.

bowlofstew/sv6,bowlofstew/sv6,bowlofstew/sv6,aclements/sv6,bowlofstew/sv6,aclements/sv6,aclements/sv6,aclements/sv6,aclements/sv6,bowlofstew/sv6