samba: apply patch mailinglist, which fixes #ifdef boundaries

http://samba.2283325.n4.nabble.com/Fix-compilation-of-Samba-4-7-4-with-disabled-ADS-td4728041.html

pkgs/servers/samba/4.x.nix

@@ -30,6 +30,7 @@ stdenv.mkDerivation rec {
 
   patches =
     [ ./4.x-no-persistent-install.patch
+      ./patch-source3__libads__kerberos_keytab.c.patch
     ];
 
   buildInputs =

pkgs/servers/samba/patch-source3__libads__kerberos_keytab.c.patch

@@ -0,0 +1,20 @@
+--- old/source3/libads/kerberos_keytab.c	2017-12-23 14:23:53.247467000 +0100
++++ new/source3/libads/kerberos_keytab.c	2017-12-23 18:57:07.135340000 +0100
+@@ -32,8 +32,6 @@
+ 
+ #ifdef HAVE_KRB5
+ 
+-#ifdef HAVE_ADS
+-
+ /* This MAX_NAME_LEN is a constant defined in krb5.h */
+ #ifndef MAX_KEYTAB_NAME_LEN
+ #define MAX_KEYTAB_NAME_LEN 1100
+@@ -85,6 +83,8 @@
+ 	return ret;
+ }
+ 
++#ifdef HAVE_ADS
++
+ /**********************************************************************
+  Adds a single service principal, i.e. 'host' to the system keytab
+ ***********************************************************************/