Auto merge of #32050 - achanda:from-slice-v4, r=alexcrichton

Add an impl for From trait

Converts a u8 slice to a Ipv4Addr
More discussion on this here: https://github.com/rust-lang/rfcs/pull/1498#issuecomment-191921655

src/libstd/net/ip.rs

@@ -279,6 +279,13 @@ impl From<u32> for Ipv4Addr {
     }
 }
 
+#[stable(feature = "from_slice_v4", since = "1.9.0")]
+impl From<[u8; 4]> for Ipv4Addr {
+    fn from(octets: [u8; 4]) -> Ipv4Addr {
+        Ipv4Addr::new(octets[0], octets[1], octets[2], octets[3])
+    }
+}
+
 impl Ipv6Addr {
     /// Creates a new IPv6 address from eight 16-bit segments.
     ///
@@ -831,6 +838,11 @@ mod tests {
         assert_eq!(Ipv4Addr::from(2130706433), a);
     }
 
+    #[test]
+    fn ipv4_from_u32_slice() {
+        assert_eq!(Ipv4Addr::from([127, 0, 0, 1]), Ipv4Addr::new(127, 0, 0, 1))
+    }
+
     #[test]
     fn ord() {
         assert!(Ipv4Addr::new(100, 64, 3, 3) < Ipv4Addr::new(192, 0, 2, 2));