Rollup merge of rust-lang#53522 - phungleson:fix-impl-from-for-addr, r=TimNN

Add doc for impl From for Addr

As part of issue rust-lang#51430 (cc @skade).

The impl is very simple, let me know if we need to go into any details.

Additionally, I added `#[inline]` for the conversion method, let me know if it is un-necessary or might break something.

Author: GuillaumeGomez

src/libstd/net/addr.rs

@@ -554,20 +554,28 @@ impl FromInner<c::sockaddr_in6> for SocketAddrV6 {
 
 #[stable(feature = "ip_from_ip", since = "1.16.0")]
 impl From<SocketAddrV4> for SocketAddr {
+    /// Converts a [`SocketAddrV4`] into a [`SocketAddr::V4`].
     fn from(sock4: SocketAddrV4) -> SocketAddr {
         SocketAddr::V4(sock4)
     }
 }
 
 #[stable(feature = "ip_from_ip", since = "1.16.0")]
 impl From<SocketAddrV6> for SocketAddr {
+    /// Converts a [`SocketAddrV6`] into a [`SocketAddr::V6`].
     fn from(sock6: SocketAddrV6) -> SocketAddr {
         SocketAddr::V6(sock6)
     }
 }
 
 #[stable(feature = "addr_from_into_ip", since = "1.17.0")]
 impl<I: Into<IpAddr>> From<(I, u16)> for SocketAddr {
+    /// Converts a tuple struct (Into<[`IpAddr`]>, `u16`) into a [`SocketAddr`].
+    ///
+    /// This conversion creates a [`SocketAddr::V4`] for a [`IpAddr::V4`]
+    /// and creates a [`SocketAddr::V6`] for a [`IpAddr::V6`].
+    ///
+    /// `u16` is treated as port of the newly created [`SocketAddr`].
     fn from(pieces: (I, u16)) -> SocketAddr {
         SocketAddr::new(pieces.0.into(), pieces.1)
     }