Fix mutability of buffers for a few send_* functions (#92)

src/socket.rs

@@ -318,7 +318,7 @@ impl Socket {
     /// `send` call.
     ///
     /// [`send`]: #method.send
-    pub fn send_with_flags(&self, buf: &mut [u8], flags: i32) -> io::Result<usize> {
+    pub fn send_with_flags(&self, buf: &[u8], flags: i32) -> io::Result<usize> {
         self.inner.send(buf, flags)
     }
 
@@ -330,7 +330,7 @@ impl Socket {
     /// [`send`]: #method.send
     /// [`out_of_band_inline`]: #method.out_of_band_inline
     #[cfg(all(feature = "all", not(target_os = "redox")))]
-    pub fn send_out_of_band(&self, buf: &mut [u8]) -> io::Result<usize> {
+    pub fn send_out_of_band(&self, buf: &[u8]) -> io::Result<usize> {
         self.inner.send(buf, MSG_OOB)
     }