ip link/addr: Add support for vrf keyword

ip link/addr: Add support for vrf keyword

Add vrf keyword to 'ip link' and 'ip addr' commands (common list code).

Allows:
1. Adding a link to a VRF
       $ ip link set NAME vrf NAME

   Removing a link from a VRF still uses 'ip link set NAME nomaster'

2. Showing links associated with a VRF:
       $ ip link show vrf NAME

3. List addresses associated with links in a VRF
       $ ip -br addr show vrf red

Signed-off-by: David Ahern <dsa@cumulusnetworks.com>