If `aux` points to data in host endianness, then the way to copy it to `count` is with `count = *(uint32_t *)&aux[4]`, or less appallingly with `memcpy`.

The original bit-shift code is the portable way to convert unaligned wire-endian data to a host integer.  So if `aux` points to data in wire endianness, then the original code is correct.

In the light of @jkbonfield's notes elsewhere on this commit, we should take care to figure out just what kind of data `aux` points to here.