rtnetlink: add keepalived rtm_protocol

Keepalived can set global static ip routes or virtual ip routes dynamically
following VRRP protocol states. Using a dedicated rtm_protocol will help
keeping track of it.

Changes in v2:
 - fix tab/space indenting

Signed-off-by: Alexandre Cassen <acassen@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>