Revert "Fix warning: no previous prototype for ... [-Wmissing-prototypes]"

This reverts commit 9918435ed70a1e386e1501982c2bbe0eed25e723.

Change-Id: I122b65ec59f48b8a21e2b43ccdad0ed146b0e78f
Reviewed-on: https://code.wireshark.org/review/3702
Reviewed-by: Anders Broman <a.broman58@gmail.com>