merge *-inline.h files with their main header

merge *-inline.h files with their main header

*-inline.h files are not very useful anymore.
In the attempt of cleaning up the code some more,
merge them into their main header files.

At the same time, move functions from forward.h
to forward.c, when they are used only in the latter.

No functional change is part of this patch.

Cc: Steffan Karger <steffan@karger.me>
Signed-off-by: Antonio Quartulli <a@unstable.cc>
Acked-by: Steffan Karger <steffan.karger@fox-it.com>
Message-Id: <20171112084830.22912-1-a@unstable.cc>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg15838.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>