Rollup merge of #39372 - seanmonstar:more-addr-froms, r=alexcrichton

A few ergonomic From impls for SocketAddr/IpAddr

My main motivation is removing things like this: `"127.0.0.1:3000".parse().unwrap()`. Instead, this now works: `SocketAddr::from(([127, 0, 0, 1], 3000))` or even `([127, 0, 0, 1], 3000).into())` when passing to a function.

src/libstd/net/ip.rs

@@ -656,6 +656,13 @@ impl From<[u8; 4]> for Ipv4Addr {
     }
 }
 
+#[stable(feature = "ip_from_slice", since = "1.17.0")]
+impl From<[u8; 4]> for IpAddr {
+    fn from(octets: [u8; 4]) -> IpAddr {
+        IpAddr::V4(Ipv4Addr::from(octets))
+    }
+}
+
 impl Ipv6Addr {
     /// Creates a new IPv6 address from eight 16-bit segments.
     ///
@@ -1186,6 +1193,21 @@ impl From<[u16; 8]> for Ipv6Addr {
     }
 }
 
+
+#[stable(feature = "ip_from_slice", since = "1.17.0")]
+impl From<[u8; 16]> for IpAddr {
+    fn from(octets: [u8; 16]) -> IpAddr {
+        IpAddr::V6(Ipv6Addr::from(octets))
+    }
+}
+
+#[stable(feature = "ip_from_slice", since = "1.17.0")]
+impl From<[u16; 8]> for IpAddr {
+    fn from(segments: [u16; 8]) -> IpAddr {
+        IpAddr::V6(Ipv6Addr::from(segments))
+    }
+}
+
 // Tests for this module
 #[cfg(all(test, not(target_os = "emscripten")))]
 mod tests {