bgpd: bgp_connect should return an `enum connect_result`

bgpd: bgp_connect should return an `enum connect_result`

This function when it is run by bgp_start is expected
to return a `enum connect_result`.  But instead
the function returns a variety of values that are
not really being checked for.  Consolidate to a correct
choice.

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