* transport.c (_stp_cmd_handler): For STP_EXIT, schedule a
work queue to do the exit functions.
(_stp_transport_close): Call work queue for STP_EXIT.
(_stp_transport_send): Call _stp_ctrl_send() like before, except
when in probe_exit(). In that case, keep retrying on send errors
until we succeed.
* transport.h (_stp_transport_write): Change to call
_stp_transport_send() for NETLINK_ONLY.
* Makefile (KDIR): set to /lib/modules/... instead of
/usr/local/src/...