iproute2: Add VF spoofchk command description to ip-link.8 man page

Add documentation for the ip link set spoof checking option.  The
expanded text section explaining the VF commands was missing this
text.
Signed-off-by: Greg Rose <gregory.v.rose@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

man/man8/ip-link.8

@@ -301,6 +301,10 @@ as 0 disables VLAN tagging and filtering for the VF.
 Setting this parameter to 0 disables rate limiting. The
 .B vf
 parameter must be specified.
+
+.sp
+.BI spoofchk " on|off"
+- turn packet spoof checking on or off for the specified VF.
 .in -8
 
 .TP