Update one of the known limitations bullet items
Update one of the known limitations bullet items

+ To FieldMatch and action Param, add controller packet metadata,
  which has the same restriction as the other two.
+ Tighten the restriction to only unsigned bitstrings, i.e. values of
  type bit<W>.  The P4Info file has only a bitwidth value to describe
  the types of these values, with no way to distinguish int<W> from
  bit<W>.

p4lang/p4runtime,p4lang/p4runtime,p4lang/p4runtime