Debian: Update package dependency

Debian: Update package dependency

Given that it is libopenvswitch-dev not libopenvswitch that depends on
libssl-dev, this patch updates debian/control file to reflect that
libopenvswitch-dev depends on libssl-dev, and libopenvswitch depends
on openssl.

Tested on Ubuntu 16.04 and 14.04.

VMWare-BZ: #1953215
CC: Ben Warren <ben@skyportsystems.com>
Fixes: c33e9122dbc3 ("Debian: Rework libopenvswitch packages")
Signed-off-by: Yi-Hung Wei <yihung.wei@gmail.com>
Acked-by: Ben Warren <ben@skyportsystems.com>
Signed-off-by: Gurucharan Shetty <guru@ovn.org>