Fix byteswapping (#99869)
On big endian systems byteswapping should be done other way around.
This change fixes TestE2ETensorPipe.TestTrainingLoop test from
test_cpp_rpc testsuite on big endian systems.
Use uint64_t when decoding double values.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/99869
Approved by: https://github.com/ezyang
