Make ENABLE_OCC no longer depend on !ENABLE_SMALL

Make ENABLE_OCC no longer depend on !ENABLE_SMALL

OCC is useful functionality which (according to LEDE devs) adds only
about 3k to the binary size - and if the embedded router folks can
afford this trade-off, everyone else can :-)

Inspired by
https://git.lede-project.org/?p=source.git;a=commit;h=b613c96d94bcdcda7abb3
be68ea1c281ce5fbb47

Signed-off-by: Gert Doering <gert@greenie.muc.de>
Acked-by: Steffan Karger <steffan.karger@fox-it.com>
Message-Id: <20170319184135.23548-1-gert@greenie.muc.de>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg14281.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>