res_format_attr_h263: Generate valid SDP fmtp for H.263+.

res_format_attr_h263: Generate valid SDP fmtp for H.263+.

Fixed:
* RFC 4629 does not allow the value "0" for MPI, K, and N.
* Allow value "0" for PAR.
* BPP is printed only when specified because "0" has a meaning.

New:
* Added CPCF and MaxBR.
* Some implementations provide CIF without MPI: a=fmtp:xx CIF;F=1
  Although a violation of RFC 3555 section 3, we can support that.

Changed:
* Resorts the CIFs from large to small which partly fixes ASTERISK~29267.

Change-Id: I95a650c715007b8dde11a77cb37d9c6c123a441e