pppx_if_find_locked
struct pppx_if *pppx_if_find_locked(struct pppx_dev *, int, int);
if ((pxi = pppx_if_find_locked(pxd, session_id, protocol)))
pxi = pppx_if_find_locked(pxd, req->pcr_session_id, req->pcr_protocol);