Documentation: fix networking related doc refs.

Signed-off-by: Tom Saeger <tom.saeger@oracle.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/networking/checksum-offloads.txt

@@ -47,7 +47,7 @@ The requirements for GSO are more complicated, because when segmenting an
  (section 'E') for more details.
 
 A driver declares its offload capabilities in netdev->hw_features; see
- Documentation/networking/netdev-features for more.  Note that a device
+ Documentation/networking/netdev-features.txt for more.  Note that a device
  which only advertises NETIF_F_IP[V6]_CSUM must still obey the csum_start
  and csum_offset given in the SKB; if it tries to deduce these itself in
  hardware (as some NICs do) the driver should check that the values in the

Documentation/networking/packet_mmap.txt

@@ -1055,7 +1055,7 @@ TX_RING part only TP_STATUS_AVAILABLE is set, then the tp_sec and tp_{n,u}sec
 members do not contain a valid value. For TX_RINGs, by default no timestamp
 is generated!
 
-See include/linux/net_tstamp.h and Documentation/networking/timestamping
+See include/linux/net_tstamp.h and Documentation/networking/timestamping.txt
 for more information on hardware timestamps.
 
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