lib: Avoid re-definition of IPPROTO_IP with some versions of Linux

* Starting from linux-4.11 [commit
  bcb41c6bced1ee778d23c53a6b4807fb08cf5540], linux/mroute.h includes
  linux/in.h , that makes gcc roar a lot of things like "error:
  redeclaration of enumerator 'IPPROTO_IP'" when compiling quagga-1.2.2

  lib/zebra.h includes sys/capability.h first, then includes
  netinet/in.h . In sys/capability.h, it includes linux/xattr.h, and
  that includes linux/libc-compat.h . Since at that time netinet/in.h is
  not included yet, _NETINET_IN_H is not defined, causing libc-compat.h
  set __UAPI_DEF_IN_IPPROTO to 1. Then, a include of netinet/in.h
  defines IPPROTO_IP. Later a include of linux/mroute.h includes
  linux/in.h. Because __UAPI_DEF_IN_IPPROTO is set to non zero,
  IPPROTO_IP is redeclared.

* lib/zebra.h: Move the privs/capabilities include block to after the
  network block.

lib/zebra.h

@@ -130,16 +130,6 @@ typedef int socklen_t;
 #endif /* !va_copy */
 #endif /* !C99 */
 
-
-#ifdef HAVE_LCAPS
-#include <sys/capability.h>
-#include <sys/prctl.h>
-#endif /* HAVE_LCAPS */
-
-#ifdef HAVE_SOLARIS_CAPABILITIES
-#include <priv.h>
-#endif /* HAVE_SOLARIS_CAPABILITIES */
-
 /* network include group */
 
 #include <sys/socket.h>
@@ -224,6 +214,16 @@ typedef int socklen_t;
 #include <netinet6/nd6.h>
 #endif /* HAVE_NETINET6_ND6_H */
 
+/* Privileges / capabilities */
+#ifdef HAVE_LCAPS
+#include <sys/capability.h>
+#include <sys/prctl.h>
+#endif /* HAVE_LCAPS */
+
+#ifdef HAVE_SOLARIS_CAPABILITIES
+#include <priv.h>
+#endif /* HAVE_SOLARIS_CAPABILITIES */
+
 /* Some systems do not define UINT32_MAX, etc.. from inttypes.h
  * e.g. this makes life easier for FBSD 4.11 users.
  */