Plenty, as the X.25 PLP implementation is CONFIG_EXPERIMENTAL.
This man page is incomplete.
There is no dedicated application programmers header file yet; you need to include the kernel header file <linux/x25.h>. CONFIG_EXPERIMENTAL might also imply that future versions of the interface are not binary compatible.
X.25 N-Reset events are not propagated to the user process yet. Thus, if a reset occurred, data might be lost without notice.