Move adjust_power_of_2() to integer.h

Move adjust_power_of_2() to integer.h

misc.c is a mess of incoherent functions, and is therefore included by
virtually all our source files.  That makes testing harder than it should
be.  As a first step of cleaning up misc.c, move adjust_power_of_2() to
integer.h, which is a more suitable place for a function like this.

This allows us to remove the duplicate implementation from test_argv.c.

Signed-off-by: Steffan Karger <steffan.karger@fox-it.com>
Acked-by: Antonio Quartulli <antonio@openvpn.net>
Message-Id: <20170621211043.6490-1-steffan@karger.me>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg14940.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>