Typo fix: change correct rule id

rules/REQUEST-921-PROTOCOL-ATTACK.conf

@@ -472,7 +472,7 @@ SecRule TX:/paramcounter_.*/ "@gt 1" \
 # closing of the array.
 # Rule 921210 PL3 prevents this by disallowing arbitrary strings after an array has
 # been closed or inbetween the square brackets in multidimensional arrays.
-# Please note that rule 921120 allows for 2-dimensional, but not for higher dimensional
+# Please note that rule 921210 allows for 2-dimensional, but not for higher dimensional
 # arrays. If these are flagged as attacks, a rule exclusion will have to be
 # deployed; ideally for the parameter(s) in question.
 #