add missing static attribute to functions

add missing static attribute to functions

Functions used only in the file where they are
defined and not exported in any header, should
always defined as static in order to make the scope
clear to the compiler and the developers.

Add the static attribute where missing.

Signed-off-by: Antonio Quartulli <antonio@openvpn.net>
Acked-by: Steffan Karger <steffan@karger.me>
Message-Id: <20170811090744.31750-4-a@unstable.cc>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg15202.html
Signed-off-by: David Sommerseth <davids@openvpn.net>
(cherry picked from commit 72bcdfdc19243c1ed6cb8568f62f0c35e8b70f5f)