timedatectl: avoid specifically referring to NTP

systemd-timesyncd not only does NTP, but also manages clock monotonicity
using a flags file. In future, it might learn PTP support. Hence don't
expose its enablement state as "NTP" but use the more generic term
"network time synchronization". After all, for similar reasons
systemd-timesyncd is not called systemd-ntpd.

man/timedatectl.xml

@@ -104,10 +104,13 @@
         <term><command>status</command></term>
 
         <listitem><para>Show current settings of the system clock and
-        RTC, including whether NTP is enabled. Note that the NTP state
+        RTC, including whether network time synchronization is
+        enabled. Note that the network time synchronization state
         simply reflects whether the
         <filename>systemd-timesyncd.service</filename> unit is
-        enabled.</para></listitem>
+        enabled. Even if the status is shown as off with this command
+        another service might still synchronize the network over the
+        network.</para></listitem>
       </varlistentry>
 
       <varlistentry>
@@ -162,11 +165,13 @@
       <varlistentry>
         <term><command>set-ntp [BOOL]</command></term>
 
-        <listitem><para>Takes a boolean argument. Controls whether NTP
-        based network time synchronization is enabled (if
-        available). This enables or disables the
-        <filename>systemd-timesyncd.service</filename>
-        unit.</para></listitem>
+        <listitem><para>Takes a boolean argument. Controls whether
+        network time synchronous is enabled (if available). This
+        enables or disables the
+        <filename>systemd-timesyncd.service</filename> unit. Note that
+        even if time synchronization is turned off with this command
+        another system service might still synchronize the clock with
+        the network.</para></listitem>
       </varlistentry>
 
     </variablelist>