man: ip-l2tp.8: fix l2spec_type documentation

Signed-off-by: Asbjørn Sloth Tønnesen <asbjorn@asbjorn.st>
diff --git a/man/man8/ip-l2tp.8 b/man/man8/ip-l2tp.8
index 5b7041f..4a3bb20 100644
--- a/man/man8/ip-l2tp.8
+++ b/man/man8/ip-l2tp.8
@@ -239,7 +239,7 @@
 set the layer2specific header type of the session.
 .br
 Valid values are:
-.BR none ", " udp "."
+.BR none ", " default "."
 .TP
 .BI offset " OFFSET"
 sets the byte offset from the L2TP header where user data starts in