bgpd: Convert `struct bgp_info` to `struct bgp_path_info`

bgpd: Convert `struct bgp_info` to `struct bgp_path_info`

Do a straight conversion of `struct bgp_info` to `struct bgp_path_info`.
This commit will setup the rename of variables as well.

This is being done because `struct bgp_info` is not descriptive
of what this data actually is.  It is path information for routes
that we keep to build the actual routes nexthops plus some extra
information.

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