Don't hardcode endianness

[lkatalin]

Use the host endianness instead of to_le_bytes() or to_be_bytes(). I think there is an easy way to do this from byteorder but I'd have to look again.

[ansasaki]

Check if this is actually valid: the encoding is kept the same independently of the arch to avoid encoding errors due to endianess. A good approach to check is to test the changes proposed in #637 mixing big endian and little endian arches