bgpd: Properly lock parent node for type4 routes

bgpd: Properly lock parent node for type4 routes

When creating a bgp_path_info for a type 4 route the pi->extra->parent
and the route node for the originating table were not being locked
properly.  This will prevent BGP from not properly cleaning up
the data structures on cleanup.

Possibly every one of the functions that we use to create the
new bgp_path_info's should use an abstracted version of this code,
but I am unsure at this point in time if a type 4 should use the same
or not.

Signed-off-by: Donald Sharp <sharpd@cumulusnetworks.com>