bgpd: Make bgp_info_cmp robust to paths that do not have su_remote info

bgpd: Make bgp_info_cmp robust to paths that do not have su_remote info

My original su_remote == NULL check is not correct. It seems that

* bgp_route.c: (bgp_info_cmp) Some bgp_info is compared with su_remote=NULL
  and it's supposed to be perfectly legal.  E.g.  configured subnet announces
  ("network a.b.c.d/n"). Ensure bgp_info_cmp is robust if such a path gets
  as far as the neighbour address comparison step.

(cherry picked from commit 2820a01eed1c616d490ddbfd17793c19597459d1)

Conflicts:
	bgpd/bgp_route.c