Plugin asterisk: fix typos for "unknown" dataset

The "draw" configuration as well as the "value" were ignored.

plugins/asterisk/asterisk

@@ -206,7 +206,7 @@ END
 print <<END;
 other.draw AREASTACK
 other.label Other known codecs
-unknwon.draw AREASTACK
+unknown.draw AREASTACK
 unknown.label Unknown codec
 END
 
@@ -309,7 +309,7 @@ if ( !$sipchannels_response and !$iaxchannels_response ) {
   }
   print <<END;
 other.value U
-unknown.valeu U
+unknown.value U
 END
 } else {
   my @results;