res_pjsip_caller_id: Copy header name to short header name

When compact_headers was set, we were sending a zero-length header name
for PAI and RPID because we always forced the short header name length
to 0.  We did this because we cloned the header from "From" and wanted
to clear "f" from the sname.  By cloning however, we bypass pjproject's
automatic logic that sets sname to name if there's no compact form of
the header, which there isn't for PAI and RPID.  So now we force sname
to be the same as name right after we set name.

res_pjsip_diversion needed the same treatment for the Diversion header.

ASTERISK-26241 #close

Change-Id: I633ec139630cd83809aae00336cee4a10077e467