message: [network] fixing bench dependency
  ```
  warning: /Users/wqfish/github/libra/network/Cargo.toml: unused manifest key: bench.0.default
  ```
  a warning slipped through, feature flags for benchmarks need to be set in dev-dependencies.
  Closes:
  Approved by: wqfish
diff: @@ -42,6 +42,7 @@ libra-proptest-helpers = { path = "../common/proptest-helpers", version = "0.1.0
  [dev-dependencies]
  criterion = "0.3.0"
  socket-bench-server = { path = "socket-bench-server", version = "0.1.0" }
  +noise = { path = "noise", version = "0.1.0", features = ["testing"] }
  [build-dependencies]
  prost-build = "0.6"
  @@ -53,7 +54,6 @@ fuzzing = ["proptest", "libra-proptest-helpers", "libra-types/fuzzing"]
  [[bench]]
  name = "socket_muxer_bench"
  harness = false
  -default = ["testing"]
  [[bench]]
  name = "network_bench"
  