docs: networking: timestamping: mention MSG_EOR flag

TCP got MSG_EOR support in linux-4.7.

This is a canonical way of making sure no coalescing
will be performed on the skb, even if it could not be
immediately sent.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Martin KaFai Lau <kafai@fb.com>
Acked-by: Willem de Bruijn <willemb@google.com>
Link: https://lore.kernel.org/r/20231212110608.3673677-1-edumazet@google.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

Documentation/networking/timestamping.rst

@@ -357,7 +357,8 @@ enabling SOF_TIMESTAMPING_OPT_ID and comparing the byte offset at
 send time with the value returned for each timestamp. It can prevent
 the situation by always flushing the TCP stack in between requests,
 for instance by enabling TCP_NODELAY and disabling TCP_CORK and
-autocork.
+autocork. After linux-4.7, a better way to prevent coalescing is
+to use MSG_EOR flag at sendmsg() time.
 
 These precautions ensure that the timestamp is generated only when all
 bytes have passed a timestamp point, assuming that the network stack