make time-related socket options overridable by arch bits files
SO_RCVTIMEO and SO_SNDTIMEO already were, but only in aggregate with SO_DEBUG and all of the other low/traditional options that varied per arch. SO_TIMESTAMP* are newly overridable. the two groups have to be done separately since mips64 and powerpc64 will override the former but not the latter. at some point this should be cleaned up to use bits headers more idiomatically.