aya: Add MapFd trait

This allows for programs to get a maps fd, like the program fd trait.

Signed-off-by: Dave Tucker <dave@dtucker.co.uk>

aya/src/maps/mod.rs

@@ -306,6 +306,18 @@ impl Drop for Map {
     }
 }
 
+/// Allows the Fd of a loaded [`Map`] to be retrieved
+pub trait MapFd {
+    /// Returns the [`RawFd`] of the program if it has been loaded, or `None`
+    fn fd(&self) -> Option<RawFd>;
+}
+
+impl MapFd for Map {
+    fn fd(&self) -> Option<RawFd> {
+        self.fd
+    }
+}
+
 /// An iterable map
 pub trait IterableMap<K: Pod, V> {
     /// Get a generic map handle