xkey_provider: fix building with --disable-management

xkey_provider: fix building with --disable-management

v2: also fix building test_provider
 - ifdefs in test_provider.c
 - include integer.h for min_int as manage.h
   may not always pull it in

Too many ifdefs, unfortunately..

Signed-off-by: Selva Nair <selva.nair@gmail.com>
Acked-by: Frank Lichtenheld <frank@lichtenheld.com>
Message-Id: <20220727221830.31861-1-selva.nair@gmail.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg24749.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>