Connect zlib to the build.
This patch fixes a problem, which exists if you have IPSEC in your kernel
and want to have crypto support loaded as KLD. By moving zlib to separate
module and adding MODULE_DEPEND directives, it is possible to use such
configuration without complication. Otherwise, since IPSEC is linked with
zlib (just like crypto.ko) you'll get following error:
interface zlib.1 already present in the KLD 'kernel'!
Approved by: cognet (mentor)
Approved by: re (scottl)