Add Socket::send_msg_with_flags and Socket::recv_msg_with_flags

Motivation: Existing methods send_msg and recv_msg do not expose
the full capabilities of the sendmsg() and recvmsg() syscalls.
Changes: Add these to methods that expose the flag argument.
Rewrite send_msg and recv_msg to use the _with_flags_version

Author: poscat0x04

library/std/src/sys/net/connection/socket/unix.rs

@@ -362,11 +362,16 @@ impl Socket {
     }
 
     #[cfg(any(target_os = "android", target_os = "linux", target_os = "cygwin"))]
-    pub fn recv_msg(&self, msg: &mut libc::msghdr) -> io::Result<usize> {
-        let n = cvt(unsafe { libc::recvmsg(self.as_raw_fd(), msg, libc::MSG_CMSG_CLOEXEC) })?;
+    pub fn recv_msg_with_flags(&self, msg: &mut libc::msghdr, flags: c_int) -> io::Result<usize> {
+        let n = cvt(unsafe { libc::recvmsg(self.as_raw_fd(), msg, flags) })?;
         Ok(n as usize)
     }
 
+    #[cfg(any(target_os = "android", target_os = "linux", target_os = "cygwin"))]
+    pub fn recv_msg(&self, msg: &mut libc::msghdr) -> io::Result<usize> {
+        self.recv_msg_with_flags(msg, libc::MSG_CMSG_CLOEXEC)
+    }
+
     pub fn peek_from(&self, buf: &mut [u8]) -> io::Result<(usize, SocketAddr)> {
         self.recv_from_with_flags(buf, MSG_PEEK)
     }
@@ -385,11 +390,16 @@ impl Socket {
     }
 
     #[cfg(any(target_os = "android", target_os = "linux", target_os = "cygwin"))]
-    pub fn send_msg(&self, msg: &libc::msghdr) -> io::Result<usize> {
-        let n = cvt(unsafe { libc::sendmsg(self.as_raw_fd(), msg, 0) })?;
+    pub fn send_msg_with_flags(&self, msg: &libc::msghdr, flags: c_int) -> io::Result<usize> {
+        let n = cvt(unsafe { libc::sendmsg(self.as_raw_fd(), msg, flags) })?;
         Ok(n as usize)
     }
 
+    #[cfg(any(target_os = "android", target_os = "linux", target_os = "cygwin"))]
+    pub fn send_msg(&self, msg: &libc::msghdr) -> io::Result<usize> {
+        self.send_msg_with_flags(msg, 0)
+    }
+
     pub fn set_timeout(&self, dur: Option<Duration>, kind: libc::c_int) -> io::Result<()> {
         let timeout = match dur {
             Some(dur) => {