net/ocserv: fix tun handoff between parent and worker process

ocserv hands off a tun fd to a worker process, but the worker process never
claims the tun with TUNSIFPID. The parent then closes the tunnel and leaves
it in a nasty state.

Bump PORTREVISION, as this is runtime breakage.

PR: 238500
Approved by: bapt (ports), cpm (maintainer, e-mail)
MFH: 2019Q4 (blanket, runtime fix)