doc: Mention MSG_ZEROCOPY implementation for UDP

MSG_ZEROCOPY implementation for UDP was merged in v5.0,
6e360f73 ("Merge branch 'udp-msg_zerocopy'").
Signed-off-by: Petr Vorel <pvorel@suse.cz>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/msg_zerocopy.rst

@@ -7,7 +7,7 @@ Intro
 =====
 
 The MSG_ZEROCOPY flag enables copy avoidance for socket send calls.
-The feature is currently implemented for TCP sockets.
+The feature is currently implemented for TCP and UDP sockets.
 
 
 Opportunity and Caveats