Introduce new IOCTL CTL_PORT_LIST reporting in more flexible XML format.

Leave old CTL_GET_PORT_LIST in place so far.  Garbage-collect it later.
When getting the initial value of numeric tunables use the
getenv_xxx() functions instead of strtoq(), because the getenv_xxx()
functions include wrappers for various postfixes like G/M/K, which
strtoq() doesn't do.