debian: Fix broken build after some man pages became generated from RST

debian: Fix broken build after some man pages became generated from RST

As far as I know, the official way to build debian packages is by invoking
following command:

> fakeroot debian/rules binary

However, that command started to fail with these errors:

dh_installman --language=C
dh_installman: Cannot find (any matches for) "utilities/ovs-appctl.8" (tried in .)
dh_installman: Cannot find (any matches for) "utilities/ovs-l3ping.8" (tried in .)
dh_installman: Cannot find (any matches for) "utilities/ovs-tcpdump.8" (tried in .)

because the generated manpages are not part of the source tree anymore.  This
patch updates debian *.manpages files to point to the generted files.

Fixes: 39b5e46312 ("Documentation: Convert multiple manpages to ReST.")
CC: Ben Pfaff <blp@ovn.org>
Signed-off-by: Ansis Atteka <aatteka@ovn.org>
Acked-by: Ben Pfaff <blp@ovn.org>