Color mode in segment routing traffic engineering using BGP

Color-only mode corresponding to color bits 01 and supports the steering fallback mechanism (in a limited manner) when color bits as set to 01 as described in IETF DRAFT-SPRING-SRTE. Use the extended-nexthop-color CLI configuration option to set color bits to 01 to enable color-only mode. Fall back to color-only SRTE policies is also supported and can be configured independently by configuring an import policy at the headend.