[package] openvpn: make comp_lzo a parameter

Possible parameters are yes, no and adaptive. See manpage for more information.

Signed-off-by: Philipp Borgers <borgers@mi.fu-berlin.de>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@38412 3c298f89-4303-0410-b956-a3cf2f4a3e73