ofp-util: Export (again) a generalized function for normalizing rules.

ofp-util: Export (again) a generalized function for normalizing rules.

Feature #5029 requests that "ovs-ofctl add-flow" report an attempt to add
a flow that is not properly normalized, that is, a flow to which the switch
will add extra wildcards, ignoring some fields specified by the user.  This
requires that ofp-util make flow normalization directly available (again).

Until now, flow normalization has only been applied to OpenFlow 1.0 flows,
but the concept applies equally to NXM, so this commit generalizes the
implementation to NXM also.