FS#2344 - add VRF support

[openwrt-bot]

n8v8R:

https://www.kernel.org/doc/Documentation/networking/vrf.txt

Virtual Routing and Forwarding (VRF) would appear to be a perfect companion for a router device, considering its benefits

• higher priority ip rules (Policy Based Routing, PBR)
• iproute2 supports the vrf
• unix socket routing
• impacts only Layer 3 and above so L2 tools (e.g., LLDP) are not affected
• VRF devices allow VRFs to be nested within namespaces

Unfortunately, support for VRF is currently absent from the OpenWRT repo in all version.

[openwrt-bot]

n8v8R:

https://github.com/torvalds/linux/blob/master/drivers/net/Kconfig#L354

config NET_VRF
tristate "Virtual Routing and Forwarding (Lite)"
depends on IP_MULTIPLE_TABLES
depends on NET_L3_MASTER_DEV
depends on IPV6 || IPV6=n
depends on IPV6_MULTIPLE_TABLES || IPV6=n
---help---
This option enables the support for mapping interfaces into VRF's. The
support enables VRF devices.