bgpd: Disable connected check for next hop on eBGP peers

bgpd: Disable connected check for next hop on eBGP peers

In the data center, in conjunction with next hop propagation for features
such as announcing VIP routes to load balancers and such, it is desired to
disable the connected route check even on ebgp peers with TTL of 1. This
patch is used to disable the check for all peers instead of the peer by
peer check that is currently supported. Furthermore, the existing
disable-connected-check is different from how Cisco implements this feature.
So, we add this new flag to avoid reliance on the existing flag.

Signed-off-by: Dinesh G Dutt <ddutt@cumulusnetworks.com>
Reviewed-by: Vivek Venkatraman <vivek@cumulusnetworks.com>