[LINTER] Replace unsigned short with uint16_t

Summary:
Similar to uint8_t, suggested by @deadalnix.

Depends on D9987.

Test Plan:

arc lint --everything

Undo any change from D9987 and Check the linter proposes a replacement.

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Subscribers: majcosta, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D9998