Revert "gnu: Remove asio-1.12."

This reverts commit e8cb755774.

The variable is still required by restbed.

gnu/packages/networking.scm

@@ -3023,17 +3023,18 @@ eight bytes) tools
     ;; Either BSD-3 or GPL-2 can be used.
     (license (list license:bsd-3 license:gpl2))))
 
-(define-public asio
+;;; This is an old version required by rested.
+(define-public asio-1.12
   (package
     (name "asio")
-    (version "1.20.0")
+    (version "1.12.2")
     (source
      (origin
        (method url-fetch)
        (uri (string-append "mirror://sourceforge/asio/asio/"
                            version " (Stable)/asio-" version ".tar.bz2"))
        (sha256
-        (base32 "0335kyxdnwnp96sh9p3jq1s87qnfmp5l7hzlcdxbbwfzrb9p8hr0"))))
+        (base32 "1akray4l3hgahmb92sbvsqg128c7g7s92jrkf1sp1fjnfjrxq9sf"))))
     (build-system gnu-build-system)
     (inputs
      `(("boost" ,boost)
@@ -3050,6 +3051,18 @@ low-level I/O programming that provides developers with a consistent
 asynchronous model using a modern C++ approach.")
     (license license:boost1.0)))
 
+(define-public asio
+  (package
+    (inherit asio-1.12)
+    (version "1.20.0")
+    (source
+     (origin
+       (method url-fetch)
+       (uri (string-append "mirror://sourceforge/asio/asio/"
+                           version " (Stable)/asio-" version ".tar.bz2"))
+       (sha256
+        (base32 "0335kyxdnwnp96sh9p3jq1s87qnfmp5l7hzlcdxbbwfzrb9p8hr0"))))))
+
 (define-public shadowsocks
   ;; There are some security fixes after the last release.
   (let* ((commit "e332ec93e9c90f1cbee676b022bf2c5d5b7b1239")