ISA endianness isn't documented

[dthaler]

See thread at https://mailarchive.ietf.org/arch/msg/bpf/EQRkTwQJRUnYQzQKsZJ6phqaAAQ/

Jose summarized:

This implies in little-endian you have 64-bit BPF instructions like: code:8 src:4 dst:4 offset:16 imm:32

and in big-endian you have 64-bit BPF instructions like: code:8 dst:4 src:4 offset:16 imm:32

where `offset' and the immediate fields are encoded in little-endian and big-endian byte-order, respectively.

Alexei states:

It's not well documented. More 'tribal knowledge', since it's carried over from cBPF.

[dthaler]

Fixed