ofp-parse: Separate fields properly.

ofp-parse: Separate fields properly.

Currently, each token in an OpenFlow match field is treated separately -
whether this is a name, a value, or a single identifier. However, this
means that attempting to get a value may result in grabbing the next
token if no value exists. This avoids that problem by breaking the match
string down into its components and then individually separating it into
name/value pairs if appropriate.

Signed-off-by: Jesse Gross <jesse@nicira.com>
Acked-by: Ben Pfaff <blp@nicira.com>