all: fix up multiple-include-guard defines

Previously, src/nm-ip4-config.h, libnm/nm-ip4-config.h, and
libnm-glib/nm-ip4-config.h all used "NM_IP4_CONFIG_H" as an include
guard, which meant that nm-test-utils.h could not tell which of them
was being included (and so, eg, if you tried to include
nm-ip4-config.h in a libnm test, it would fail to compile because
nm-test-utils.h was referring to symbols in src/nm-ip4-config.h).

Fix this by changing the include guards in the non-API-stable parts of
the tree:

  - libnm-glib/nm-ip4-config.h remains   NM_IP4_CONFIG_H
  - libnm/nm-ip4-config.h now uses     __NM_IP4_CONFIG_H__
  - src/nm-ip4-config.h now uses       __NETWORKMANAGER_IP4_CONFIG_H__

And likewise for all other headers.

The two non-"nm"-prefixed headers, libnm/NetworkManager.h and
src/NetworkManagerUtils.h are now __NETWORKMANAGER_H__ and
__NETWORKMANAGER_UTILS_H__ respectively, which, while not entirely
consistent with the general scheme, do still mostly make sense in
isolation.

src/NetworkManagerUtils.h

@@ -19,8 +19,8 @@
  * Copyright (C) 2005 - 2008 Novell, Inc.
  */
 
-#ifndef NETWORK_MANAGER_UTILS_H
-#define NETWORK_MANAGER_UTILS_H
+#ifndef __NETWORKMANAGER_UTILS_H__
+#define __NETWORKMANAGER_UTILS_H__
 
 #include <glib.h>
 #include <stdio.h>
@@ -162,4 +162,4 @@ void nm_utils_ipv6_addr_set_interface_identfier (struct in6_addr *addr,
 void nm_utils_ipv6_interface_identfier_get_from_addr (NMUtilsIPv6IfaceId *iid,
                                                       const struct in6_addr *addr);
 
-#endif /* NETWORK_MANAGER_UTILS_H */
+#endif /* __NETWORKMANAGER_UTILS_H__ */