bgpd: resolve memleak on show bgp vrf all ipv6 unicast summary json

bgpd: resolve memleak on show bgp vrf all ipv6 unicast summary json

Problem reported with memory leak when the command "show bgp vrf all
ipv6 unicast summary json" is issued.  Found that the problem only
occurs if the configuration does not actually include the ipv6
address-family but does contain ipv4 unicast peers. If we didn't
match a peer in the address-family being displayed, we would create
the json object but never free it.  This fix actually stops creating
the json object in this section of code and lets the create happen
in the area where the match occurs.

Ticket: CM-25616
Signed-off-by: Don Slice <dslice@cumulusnetworks.com>