nm: Check for libnm

libnm replaces libnm-glib. This will make sense with port to libnm and is done
to reduce line noise in that commit.

src/frontends/gnome/auth-dialog/Makefile.am

@@ -4,8 +4,7 @@ nm_strongswan_auth_dialog_CPPFLAGS = \
 	$(GTK_CFLAGS) \
 	$(LIBGNOMEUI_CFLAGS) \
 	$(LIBSECRET_CFLAGS) \
-	$(NETWORK_MANAGER_CFLAGS) \
-	$(NM_UTILS_CFLAGS) \
+	$(LIBNM_GLIB_CFLAGS) \
 	-DG_DISABLE_DEPRECATED \
 	-DGNOME_DISABLE_DEPRECATED \
 	-DGNOMELOCALEDIR=\"$(datadir)/locale\" \
@@ -18,4 +17,4 @@ nm_strongswan_auth_dialog_LDADD = \
 	$(GTK_LIBS) \
 	$(LIBGNOMEUI_LIBS) \
 	$(LIBSECRET_LIBS) \
-	$(NM_UTILS_LIBS)
+	$(LIBNM_GLIB_LIBS)