bump silk
bump silk

[#144881385]

Submodule src/code.cloudfoundry.org/silk 9b6f0da..3bccf98:
  > controller tests case when leases on different networks
  > Acquire only re-uses leases still in the network
  > Daemon skips routes for subnets outside of overlay

cloudfoundry-incubator/cf-networking-release,cloudfoundry-incubator/cf-networking-release,cloudfoundry-incubator/cf-networking-release,cloudfoundry-incubator/cf-networking-release