Add missing mstcpip feature flag to winapi dependency.

(cherry picked from commit a7e61db9e3c2b929ef1a33532bfcc22045d163ce)
diff --git a/Cargo.toml b/Cargo.toml
index 3aedc7f..81154ae 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -57,7 +57,7 @@
 
 [target.'cfg(windows)'.dependencies]
 miow   = "0.3.6"
-winapi = { version = "0.3", features = ["winsock2", "mswsock"] }
+winapi = { version = "0.3", features = ["winsock2", "mswsock", "mstcpip"] }
 ntapi  = "0.3"
 
 [dev-dependencies]