gnu: net-tools: Add a test-only variant and use it for GnuTLS.

* gnu/packages/linux.scm (net-tools-for-tests): Add hidden net-tools variant.
* gnu/packages/tls.scm (gnutls)[native-inputs]: Use net-tools-for-tests instead
of net-tools.

gnu/packages/linux.scm

@@ -1288,6 +1288,9 @@ network hardware types (plipconfig, slattach) and advanced aspects of IP
 configuration (iptunnel, ipmaddr).")
     (license license:gpl2+)))
 
+(define-public net-tools-for-tests
+  (hidden-package net-tools))
+
 (define-public libcap
   (package
     (name "libcap")

gnu/packages/tls.scm

@@ -140,6 +140,9 @@ coordinating the use of PKCS#11 by different components or libraries
 living in the same process.")
     (license license:bsd-3)))
 
+
+;; TODO Add net-tools-for-tests to #:disallowed-references when we can afford
+;; rebuild GnuTLS (i.e. core-updates).
 (define-public gnutls
   (package
     (name "gnutls")
@@ -194,7 +197,7 @@ living in the same process.")
                "debug"
                "doc"))                            ;4.1 MiB of man pages
     (native-inputs
-     `(("net-tools" ,net-tools)
+     `(("net-tools" ,net-tools-for-tests)
        ("pkg-config" ,pkg-config)
        ("which" ,which)))
     (inputs