Consistently use the byteorder functions in the correct direction

Though ntohs and htons are functionally identical, they have different meanings.Using the correct one helps to document the code.

Submitted by: Ján Sučan <sucanjan@gmail.com>
MFC after: 2 weeks
Sponsored by: Google, inc. (Google Summer of Code 2019)
Differential Revision: https://reviews.freebsd.org/D21219