Eliminate some more `transmute()` (#8879)

* eliminate some more transmute()

* Address `review comments`

* Make unsafe block smaller
* Use different byte-order than `std`, read words as big endian instead
of little endian!

* Fix IpAddresses nits

* Use `from_be` to work both for big and little endian
* Ipv6 addresses were incorrectly `transmuted`

* remove needless lifetime annotation