chan_sip: Isolate code that manages struct sip_route.

* Move route code to sip/route.c + sip/include/route.h
* Rename functions to sip_route_*
* Replace ad-hoc list code with macro's from linkedlists.h
* Create sip_route_process_header() to processes Path and Record-Route headers
  (previously done with different code in build_route and build_path)
* Add use of const where possible
* Move struct uriparams, struct contact and contactliststruct from sip.h to
  reqresp_parser.h.  sip/route.c uses reqresp_parser.h but not sip.h, this was
  a problem.  These moved declares are not used outside of reqresp_parser.
* While modifying reqprep() the lack of {} caused me trouble.  I added them.
* Code outside route.c treats sip_route as an opaque structure, using macro's
  or procedures for all access.

(closes issue ASTERISK-22582)
Reported by: Corey Farrell
Review: https://reviewboard.asterisk.org/r/3173/


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@407926 65c4cc65-6c06-0410-ace0-fbb531ad65f3