testbench: json_eq tool does not detect extra parameters

[rgerhards]

if there is an extra parameter present, json_eq ignores it and reports "successful match".

Sample:

execute 'iptables: IN= SECOND=test'
assert_output_json_eq '{ "field": { "IN": ""} }'

gives

Out:
{ "field": { "IN": "", "SECOND": "test" } }

without any error indication.

[rgerhards]

Note: when fixed, check the testbench tests for v2-iptables parser. This may also be used during fixing.