Disable chunked transfer encoding for SOAP requests.

miniupnpd is a gigantic steaming pile of shit, and ignores the
"Transfer-Encoding" header in blatant disregard of RFC 2616.  It
doesn't support "chunked" transfer-coding either (obviously).

  All HTTP/1.1 applications that receive entities MUST accept the
  "chunked" transfer-coding (section 3.6), thus allowing this mechanism
  to be used for messages when the message length cannot be determined
  in advance.

Naturally the SOAP Fault returned when this happens is not helpful at
all.