Make system_name available for CDB list matching

[labrown]

I have a use case where I need to be able to do a CDB list lookup based on the 'system_name' decoded from Windows server logs, but that is not an available variable for CDB lists.

[jrossi]

https://github.com/ossec/ossec-hids/blob/master/src/analysisd/analysisd.c#L1365
https://github.com/ossec/ossec-hids/blob/master/src/analysisd/analysisd.c#L1373

ossec-hids/src/analysisd/decoders/decoder.c

Line 382 in eb69de7

lf->systemname = field;

ossec-hids/src/analysisd/rules.h

Line 52 in eb69de7

#define RULE_HOSTNAME 256

would be the starting point of adding this. No logic changes would be needed. If you run into problems I would be happy to help.