libnetwork/diagnostic: EnableDiagnostic(): use net.JoinHostPort
libnetwork/diagnostic: EnableDiagnostic(): use net.JoinHostPort

Use net.JoinHostPort to account for IPv6 addresses.

Signed-off-by: Sebastiaan van Stijn <64b2b6d12bfe4baae7dad3d018f8cbf6b0e7a044@gone.nl>

Ramzec/docker,thaJeztah/docker,jimjag/docker,moul/docker,trebonian/docker,trebonian/docker,mahak/docker,thaJeztah/docker,moul/docker,moby/moby,cpuguy83/docker,cpuguy83/docker,moul/docker,moul/docker,thaJeztah/docker,Ramzec/docker,konstruktoid/docker-upstream,trebonian/docker,jimjag/docker,Mokolea/docker,trebonian/docker,Ramzec/docker,Mokolea/docker,jimjag/docker,konstruktoid/docker-upstream,jimjag/docker,thaJeztah/docker,moby/moby,mahak/docker,cpuguy83/docker,Mokolea/docker,konstruktoid/docker-upstream,mahak/docker,cpuguy83/docker,moby/moby,Ramzec/docker,konstruktoid/docker-upstream,mahak/docker,Mokolea/docker,moby/moby