BUG/MINOR: h3: close connection on header list too big

BUG/MINOR: h3: close connection on header list too big

When parsing a HTX response, if too many headers are present, stop
sending and close the connection with error code H3_INTERNAL_ERROR.

Previously, no error was reported despite the interruption of header
parsing. This cause an infinite loop. However, this is considered as
minor as it happens on the response path from backend side.

This should be backported up to 2.6.
It relies on previous commit
  "MINOR: h3: check connection error during sending".