tests: Fix flaky "Routing protocol control plane redirect" test.

The test was incorrectly checking SB logical flows without waiting for
northd to actually run and reconcile the contents of the SB with what
had changed in the NB database.

Hit in ovsrobot's CI:
https://github.com/ovsrobot/ovn/actions/runs/32013870785/job/95339930296#step:13:5814

Fixes: 3705276 ("northd: Routing protocol port redirection.")
Acked-by: Ales Musil <amusil@redhat.com>
Signed-off-by: Dumitru Ceara <dceara@redhat.com>
(cherry picked from commit c60a7af)

Author: dceara

tests/ovn-northd.at

@@ -14988,6 +14988,8 @@ check ovn-nbctl ls-add ls -- \
 check ovn-nbctl lsp-add ls lsp-bgp -- \
     lsp-set-addresses lsp-bgp unknown
 
+check ovn-nbctl --wait=sb sync
+
 # Function that ensures that no redirect rules are installed.
 check_no_redirect() {
     AT_CHECK([ovn-sbctl dump-flows ls | grep ls_in_l2_lkup  | grep -E "tcp.dst == 179|tcp.src == 179" | wc -l], [0], [0