ovs-ofctl: Report attempts to add (remove, etc.) non-normalized flows.

ovs-ofctl: Report attempts to add (remove, etc.) non-normalized flows.

Commit 0b3f27253 (ovs-ofctl: Warn about flows not in normal form) made
ovs-ofctl warn about non-normalized flows, that is, flows some of whose
specified fields will be ignored by the switch.  This was convenient for
users, who are understandably confused by flow normalization.  However,
later commit 8050b31d6 (ofp-parse: Refactor flow parsing) accidentally
deleted the warning.  This commit restores it and adds a test to ensure
that it doesn't get deleted again later.

Reported-by: Reid Price <reid@nicira.com>
Bug #5029.