netfilter: nf_ct_sip: fix SDP parsing in TCP SIP messages for some Cisco phones

[ Upstream commit e6e4d9ed11fb1fab8b3256a3dc14d71b5e984ac4 ]

Some Cisco phones do not place the Content-Length field at the end of the
SIP message. This is valid, due to a misunderstanding of the specification
the parser expects the SDP body to start directly after the Content-Length
field. Fix the parser to scan for \r\n\r\n to locate the beginning of the
SDP body.

Reported-by: Teresa Kang <teresa_kang@gemtek.com.tw>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>