net: Fix minor code bug in timestamping.txt

Passing (void*)val instead of &val would make a pointer out of an integer
and cause sock_setsockopt to -EFAULT.

See tools/testing/selftests/networking/timestamping/timestamping.c
for a working example.

Cc: David S. Miller <davem@davemloft.net>
Cc: netdev@vger.kernel.org
Signed-off-by: NAhmad Fatoum <ahmad@a3f.at>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Documentation/networking/timestamping.txt

@@ -44,8 +44,7 @@ timeval of SO_TIMESTAMP (ms).
 Supports multiple types of timestamp requests. As a result, this
 socket option takes a bitmap of flags, not a boolean. In
 
-  err = setsockopt(fd, SOL_SOCKET, SO_TIMESTAMPING, (void *) val,
-                   sizeof(val));
+  err = setsockopt(fd, SOL_SOCKET, SO_TIMESTAMPING, &val, sizeof(val));
 
 val is an integer with any of the following bits set. Setting other
 bit returns EINVAL and does not change the current state.
@@ -249,8 +248,7 @@ setsockopt to receive timestamps:
 
   __u32 val = SOF_TIMESTAMPING_SOFTWARE |
 	      SOF_TIMESTAMPING_OPT_ID /* or any other flag */;
-  err = setsockopt(fd, SOL_SOCKET, SO_TIMESTAMPING, (void *) val,
-                   sizeof(val));
+  err = setsockopt(fd, SOL_SOCKET, SO_TIMESTAMPING, &val, sizeof(val));
 
 
 1.4 Bytestream Timestamps