nmcli: add get_env_flags() accessor to NMMetaEnvironment for checking offline mode

We will want to know whether we are in offline mode.
Add an accessor to get environment flags, which libnmc-setting
can use.

src/libnmc-setting/nm-meta-setting-desc.h

@@ -486,6 +486,11 @@ typedef enum {
     NM_META_ENV_WARN_LEVEL_WARN,
 } NMMetaEnvWarnLevel;
 
+typedef enum {
+    NM_META_ENV_FLAGS_NONE    = 0,
+    NM_META_ENV_FLAGS_OFFLINE = 0x1,
+} NMMetaEnvFlags;
+
 /* the settings-meta data is supposed to be independent of an actual client
  * implementation. Hence, there is a need for hooks to the meta-data.
  * The meta-data handlers may call back to the environment with certain
@@ -506,8 +511,20 @@ struct _NMMetaEnvironment {
     struct _NMRemoteConnection *const *(*get_nm_connections)(const NMMetaEnvironment *environment,
                                                              gpointer environment_user_data,
                                                              guint   *out_len);
+
+    NMMetaEnvFlags (*get_env_flags)(const NMMetaEnvironment *environment,
+                                    gpointer                 environment_user_data);
 };
 
+static inline NMMetaEnvFlags
+nm_meta_environment_get_env_flags(const NMMetaEnvironment *environment,
+                                  gpointer                 environment_user_data)
+{
+    if (environment && environment->get_env_flags)
+        return environment->get_env_flags(environment, environment_user_data);
+    return NM_META_ENV_FLAGS_NONE;
+}
+
 /*****************************************************************************/
 
 /* NMSettingBond is special in that it has nested properties.

src/nmcli/settings.c

@@ -488,12 +488,23 @@ _env_get_nm_connections(const NMMetaEnvironment *environment,
     return (NMRemoteConnection *const *) values->pdata;
 }
 
+static NMMetaEnvFlags
+_env_get_env_flags(const NMMetaEnvironment *environment, gpointer environment_user_data)
+{
+    NmCli *nmc = environment_user_data;
+
+    nm_assert(nmc);
+
+    return (nmc->offline ? NM_META_ENV_FLAGS_OFFLINE : NM_META_ENV_FLAGS_NONE);
+}
+
 /*****************************************************************************/
 
 const NMMetaEnvironment *const nmc_meta_environment = &((NMMetaEnvironment){
     .warn_fcn           = _env_warn_fcn_handle,
     .get_nm_devices     = _env_get_nm_devices,
     .get_nm_connections = _env_get_nm_connections,
+    .get_env_flags      = _env_get_env_flags,
 });
 
 static char *