pbrd: Add PBR to FRR

pbrd: Add PBR to FRR

This is an implementation of PBR for FRR.

This implemenation uses a combination of rules and
tables to determine how packets will flow.

PBR introduces a new concept of 'nexthop-groups' to
specify a group of nexthops that will be used for
ecmp.  Nexthop-groups are specified on the cli via:

nexthop-group DONNA
  nexthop 192.168.208.1
  nexthop 192.168.209.1
  nexthop 192.168.210.1
!

PBR sees the nexthop-group and installs these as a default
route with these nexthops starting at table 10000
robot# show pbr nexthop-groups
Nexthop-Group: DONNA Table: 10001 Valid: 1 Installed: 1
	Valid: 1  nexthop 192.168.209.1
	Valid: 1  nexthop 192.168.210.1
	Valid: 1  nexthop 192.168.208.1

I have also introduced the ability to specify a table
in a 'show ip route table XXX' to see the specified tables.

robot# show ip route table 10001
Codes: K - kernel route, C - connected, S - static, R - RIP,
       O - OSPF, I - IS-IS, B - BGP, P - PIM, E - EIGRP, N - NHRP,
       T - Table, v - VNC, V - VNC-Direct, A - Babel, D - SHARP,
       F - PBR,
       > - selected route, * - FIB route

F>* 0.0.0.0/0 [0/0] via 192.168.208.1, enp0s8, 00:14:25
  *                 via 192.168.209.1, enp0s9, 00:14:25
  *                 via 192.168.210.1, enp0s10, 00:14:25

PBR tracks PBR-MAPS via the pbr-map command:

!
pbr-map EVA seq 10
  match src-ip 4.3.4.0/24
  set nexthop-group DONNA
!
pbr-map EVA seq 20
  match dst-ip 4.3.5.0/24
  set nexthop-group DONNA
!

pbr-maps can have 'match src-ip <prefix>' and 'match dst-ip <prefix>'
to affect decisions about incoming packets.  Additionally if you
only have one nexthop to use for a pbr-map you do not need
to setup a nexthop-group and can specify 'set nexthop XXXX'.

To apply the pbr-map to an incoming interface you do this:

interface enp0s10
 pbr-policy EVA
!

When a pbr-map is applied to interfaces it can be installed
into the kernel as a rule:

[sharpd@robot frr1]$ ip rule show
0:	from all lookup local
309:	from 4.3.4.0/24 iif enp0s10 lookup 10001
319:	from all to 4.3.5.0/24 iif enp0s10 lookup 10001
1000:	from all lookup [l3mdev-table]
32766:	from all lookup main
32767:	from all lookup default

[sharpd@robot frr1]$ ip route show table 10001
default proto pbr metric 20
	nexthop via 192.168.208.1 dev enp0s8 weight 1
	nexthop via 192.168.209.1 dev enp0s9 weight 1
	nexthop via 192.168.210.1 dev enp0s10 weight 1

The linux kernel now will use the rules and tables to properly
apply these policies.

Signed-off-by: Donald Sharp <sharpd@cumulusnetworks.com>
Signed-off-by: Don Slice <dslice@cumulusnetworks.com>
Signed-off-by: Quentin Young <qlyoung@cumulusnetworks.com>