Update zero_copy(9) man page to note the renamed kernel options

and to warn about unsafeness of COW based sends.

share/man/man9/zero_copy.9

@@ -25,7 +25,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd December 5, 2004
+.Dd October 23, 2012
 .Dt ZERO_COPY 9
 .Os
 .Sh NAME
@@ -33,7 +33,8 @@
 .Nm zero_copy_sockets
 .Nd "zero copy sockets code"
 .Sh SYNOPSIS
-.Cd "options ZERO_COPY_SOCKETS"
+.Cd "options SOCKET_SEND_COW"
+.Cd "options SOCKET_RECV_PFLIP"
 .Sh DESCRIPTION
 The
 .Fx
@@ -155,6 +156,8 @@ variables respectively.
 .Xr sendfile 2 ,
 .Xr socket 2 ,
 .Xr ti 4
+.Sh BUGS
+The COW based send mechanism is not safe and may result in kernel crashes.
 .Sh HISTORY
 The zero copy sockets code first appeared in
 .Fx 5.0 ,