ofp-parse: Fix match parsing with [x..y]=z format.

ofp-parse: Fix match parsing with [x..y]=z format.

Commit 21b2fa617126 ("ofp-parse: Allow match field names in actions
and brackets in matches.") added support for matching a consecutive
set of bits with the [x..y]=z format, but the copying of the parsed
value ('z') to the match was done from a wrong offset, so that the
actual value matched would be incorrect.

Fix this and add a test case preventing regression in future.

Fixes: 21b2fa617126 ("ofp-parse: Allow match field names in actions and brackets in matches.")
Signed-off-by: Jarno Rajahalme <jarno@ovn.org>
Acked-by: Ben Pfaff <blp@ovn.org>