Print igp_metric in show route output even if AIGP is set

Hello BIRD team! This patches (for master branch) modifies the output of the show route CLI command for BGP routes to always print the IGP metric value. In current BIRD, the IGP metric is only displayed if the AIGP attribute is not set. Example, current BIRD: 10.0.0.0/8 unicast [blabla] * (100/210) [AS12322i] And with the patch: 10.0.0.0/8 unicast [blabla] * (100/10/210) [AS12322i] Even with AIGP it can be useful to see the IGP metric for each routes to troubleshoot routing issues (BGP best path selection can still consider IGP metric for routes with identical AIGP value). Thanks! -- Sébastien