[Varnish] #1329: Option to respect X-Forwarded-For header in varnishncsa

[Varnish]

#1329: Option to respect X-Forwarded-For header in varnishncsa
----------------------+-------------------------
 Reporter:  mhelmich  |       Type:  enhancement
   Status:  new       |   Priority:  normal
Milestone:            |  Component:  varnishncsa
  Version:  3.0.4     |   Severity:  minor
 Keywords:            |
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 While varnishncsa offers a "-f" flag in order to respect a X-Forwarded-For
 request header, this flag implies a fixed log line format and cannot be
 used in conjunction with "-F".

 The attached commit changes the "-f" behaviour causing varnishncsa to use
 the value from the X-Forwarded-For header (if present) instead of the
 client IP while allowing a custom log format at the same time. No change
 to the log line format is required anymore, the forwarded address will be
 inserted into the %h placeholder.

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Ticket URL: <https://www.varnish-cache.org/trac/ticket/1329>
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