get/setsockopt: add fallback for new time64 SO_RCVTIMEO/SO_SNDTIMEO

get/setsockopt: add fallback for new time64 SO_RCVTIMEO/SO_SNDTIMEO

without this, the SO_RCVTIMEO and SO_SNDTIMEO socket options would
stop working on pre-5.1 kernels after time_t is switched to 64-bit and
their values are changed to the new time64 versions.

new code is written such that it's statically unreachable on 64-bit
archs, and on existing 32-bit archs until the macro values are changed
to activate 64-bit time_t.