Fix common misspellings

Fixes generated by 'codespell' and manually reviewed.

Signed-off-by: Lucas De Marchi <lucas.demarchi@profusion.mobi>
diff --git a/include/net/pkt_sched.h b/include/net/pkt_sched.h
index d9549af..65afc49 100644
--- a/include/net/pkt_sched.h
+++ b/include/net/pkt_sched.h
@@ -32,7 +32,7 @@
    
    The result: [34]86 is not good choice for QoS router :-(
 
-   The things are not so bad, because we may use artifical
+   The things are not so bad, because we may use artificial
    clock evaluated by integration of network data flow
    in the most critical places.
  */