tests: run fewer rate-slop tests

tests/test-21-rate-slop

@@ -13,9 +13,7 @@ function try_tx_rx_rate
     ./self-test testdata-ascii.txt $txr -- $rx_rate || let fail++
 }
 
-for adj in  \
-    	-8 -7 -6 -5 -4 -3 -2 -1 \
-	0 +1 +2 +3 +4 +5 +6 +7 +8
+for adj in  -8 -5 -3 -2 -1 0 +1 +2 +3 +5 +8
 do
     let tx_rate="rx_rate + adj"
     try_tx_rx_rate $tx_rate
@@ -23,8 +21,8 @@ done
 
 if [ $fail -eq 0 ]
 then
-echo "  (all $count passed)"
+echo "  (all $count rate-slop tests passed)"
 else
-echo "  ($fail/$count failed)"
+echo "  ($fail/$count rate-slop tests failed)"
 fi
 exit $fail