BGP: support for addpath TX

BGP: support for addpath TX

Signed-off-by: Daniel Walton <dwalton@cumulusnetworks.com>
Reviewed-by:   Donald Sharp <sharpd@cumulusnetworks.com>
Reviewed-by:   Vivek Venkataraman <vivek@cumulusnetworks.com
Ticket: CM-8014

This implements addpath TX with the first feature to use it
being "neighbor x.x.x.x addpath-tx-all-paths".

One change to show output is 'show ip bgp x.x.x.x'.  If no addpath-tx
features are configured for any peers then everything looks the same
as it is today in that "Advertised to" is at the top and refers to
which peers the bestpath was advertise to.

root@superm-redxp-05[quagga-stash5]# vtysh -c 'show ip bgp 1.1.1.1'
BGP routing table entry for 1.1.1.1/32
Paths: (6 available, best #6, table Default-IP-Routing-Table)
  Advertised to non peer-group peers:
  r1(10.0.0.1) r2(10.0.0.2) r3(10.0.0.3) r4(10.0.0.4) r5(10.0.0.5) r6(10.0.0.6) r8(10.0.0.8)
  Local, (Received from a RR-client)
    12.12.12.12 (metric 20) from r2(10.0.0.2) (10.0.0.2)
      Origin IGP, metric 0, localpref 100, valid, internal
      AddPath ID: RX 0, TX 8
      Last update: Fri Oct 30 18:26:44 2015
[snip]

but once you enable an addpath feature we must display "Advertised to" on a path-by-path basis:

superm-redxp-05# show ip bgp 1.1.1.1/32
BGP routing table entry for 1.1.1.1/32
Paths: (6 available, best #6, table Default-IP-Routing-Table)
  Local, (Received from a RR-client)
    12.12.12.12 (metric 20) from r2(10.0.0.2) (10.0.0.2)
      Origin IGP, metric 0, localpref 100, valid, internal
      AddPath ID: RX 0, TX 8
      Advertised to: r8(10.0.0.8)
      Last update: Fri Oct 30 18:26:44 2015

  Local, (Received from a RR-client)
    34.34.34.34 (metric 20) from r3(10.0.0.3) (10.0.0.3)
      Origin IGP, metric 0, localpref 100, valid, internal
      AddPath ID: RX 0, TX 7
      Advertised to: r8(10.0.0.8)
      Last update: Fri Oct 30 18:26:39 2015

  Local, (Received from a RR-client)
    56.56.56.56 (metric 20) from r6(10.0.0.6) (10.0.0.6)
      Origin IGP, metric 0, localpref 100, valid, internal
      AddPath ID: RX 0, TX 6
      Advertised to: r8(10.0.0.8)
      Last update: Fri Oct 30 18:26:39 2015

  Local, (Received from a RR-client)
    56.56.56.56 (metric 20) from r5(10.0.0.5) (10.0.0.5)
      Origin IGP, metric 0, localpref 100, valid, internal
      AddPath ID: RX 0, TX 5
      Advertised to: r8(10.0.0.8)
      Last update: Fri Oct 30 18:26:39 2015

  Local, (Received from a RR-client)
    34.34.34.34 (metric 20) from r4(10.0.0.4) (10.0.0.4)
      Origin IGP, metric 0, localpref 100, valid, internal
      AddPath ID: RX 0, TX 4
      Advertised to: r8(10.0.0.8)
      Last update: Fri Oct 30 18:26:39 2015

  Local, (Received from a RR-client)
    12.12.12.12 (metric 20) from r1(10.0.0.1) (10.0.0.1)
      Origin IGP, metric 0, localpref 100, valid, internal, best
      AddPath ID: RX 0, TX 3
      Advertised to: r1(10.0.0.1) r2(10.0.0.2) r3(10.0.0.3) r4(10.0.0.4) r5(10.0.0.5) r6(10.0.0.6) r8(10.0.0.8)
      Last update: Fri Oct 30 18:26:34 2015

superm-redxp-05#