[sr-dev] couple of xavp questions

[jh at tutpro.com]

i'm trying to use xavps in new version of t serial functions and have
a couple of questions:

- when xavp value of type SR_XTYPE_STR is added using xavp_add_value
  function, do i need to make a copy of the string using pkg_malloc?  in
  normal avps this is not needed, but for some reason a copy is made in
  sql_api.c.

- what is xavp equivalent of usr_avp avp_destroy, which takes one
  argument: pointer to usr_avp to be destroyed?  there is xavp_rm, but
  it takes two arguments and i didn't find from the sources any example
  of its use.

-- juha