[Varnish] #1683: varnishncsa should log the last value in vcl sub

[Varnish]

#1683: varnishncsa should log the last value in vcl sub
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 Reporter:  razvanphp  |       Type:  defect
   Status:  new        |   Priority:  normal
Milestone:             |  Component:  build
  Version:  4.0.3      |   Severity:  normal
 Keywords:             |
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 Related to Ticket #1462, there is another case when varnishncsa does not
 log changed header values, that is when we set a header twice or overwrite
 it in vcl_recv.

 For example:  https://github.com/varnish/varnish-
 devicedetect/blob/master/devicedetect.vcl

 In this case, we can never log the correct device of the user, because
 varnishncsa will only pick the first one (pc). I think it makes more sense
 to use the LAST value.

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Ticket URL: <https://www.varnish-cache.org/trac/ticket/1683>
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