Implements recvmmsg() for UDP packets (#1161)

* Implemented recvmmsg() for UDP packets

- This change implements binding between libc API for recvmmsg()
- The function can receive multiple packets using one system call

Fixes #1141

* Added unit tests for recvmmsg()

* Added recv_mmsg() wrapper for non Linux OS

* Address review comments for recvmmsg()

* Remove unnecessary imports

* Moved target specific dependencies to the function

src/lib.rs

@@ -36,6 +36,7 @@ pub mod packet;
 pub mod payment_plan;
 pub mod record_stage;
 pub mod recorder;
+pub mod recvmmsg;
 pub mod replicate_stage;
 pub mod request;
 pub mod request_processor;
@@ -69,6 +70,7 @@ extern crate jsonrpc_core;
 #[macro_use]
 extern crate jsonrpc_macros;
 extern crate jsonrpc_http_server;
+extern crate libc;
 #[macro_use]
 extern crate log;
 extern crate nix;