tools: correct frr-reload.py handling of bgp vni/exit-vni config

tools: correct frr-reload.py handling of bgp vni/exit-vni config

Problem reported that when a peer-group was added in certain
configurations, it would be rejected because of the order of the
commands put in by nclu. Issued turned out to be how frr-reload.py
was handling the sub-sub-context of the vni under the address-family
and subsequently how it handled the following exit-vni.

Ticket: CM-21996
Signed-off-by: Don Slice <dslice@cumulusnetworks.com>