tests: fixed "ovn-controller port security OF flows"

The order of Port Binding key generation is not guaranteed, and
it might happen that sw0p1 and sw0p2 get different value than
the hardcoded 1 and 2 (e.g. 2 and 1).
Get the value from DB instead.

In addition, move "check_port_sec_offlows" definition
before it is being used the first time.

Fixes: 8cab00b ("ovn-controller: Add OF rules for port security.")
Signed-off-by: Xavier Simonart <xsimonar@redhat.com>
Signed-off-by: Dumitru Ceara <dceara@redhat.com>
(cherry picked from commit 32863e7)