gnu: liblinphone: Restore special openldap variant.

This is a partial revert of commit f2166cface.

* gnu/packages/openldap.scm (openldap-for-linphone): Restore this variable.
* gnu/packages/linphone.scm (liblinphone)[inputs]: Replace openldap with
openldap-for-linphone.

gnu/packages/linphone.scm

@@ -800,7 +800,7 @@ (define-public liblinphone
            libnotify
            libxml2
            mediastreamer2
-           openldap
+           openldap-for-linphone
            ortp
            soci
            sqlite

gnu/packages/openldap.scm

@@ -113,6 +113,21 @@ (define-public openldap
     (license openldap2.8)
     (home-page "https://www.openldap.org/")))
 
+(define-public openldap-for-linphone
+  (package
+    (inherit openldap)
+    (name "openldap")
+    (version "2.6.4")
+    (source (origin
+              (method git-fetch)
+              (uri (git-reference
+                    (url "https://gitlab.linphone.org/BC/public/external/openldap/")
+                    (commit "8a885896a3fb88098d970ab96316c0b7f18367b8")))
+              (file-name (git-file-name name version))
+              (sha256
+               (base32
+                "1yd3cnngr5z3nymnml8fynspxgdzap7y7glp601nbkdj67wyg0k8"))))))
+
 (define-public nss-pam-ldapd
   (package
     (name "nss-pam-ldapd")