For Zephyr, we allocate memory for a thread's stack from the heap.
Recently a thread's stack size was changed from 24k to 48k. wolfSSH
needed the size of the libc memory arena to be increased a bit to
account for this change.
Modify the SFTP tests to use the file configure.ac instead of configure.
Some environments do not have or use configure. Configure.ac is in the
source archive.