syscalls.master: Allow clock_nanosleep in capability mode

It is akin to nanosleep(2) and does not access global namespaces.
It should be permitted in capability mode.

Reviewed by: vangyzen
Fixes: 3f8455b090 ("Add clock_nanosleep()")
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D57343

sys/kern/syscalls.master

@@ -1430,7 +1430,7 @@
 		    _Out_ _Contains_timet_ struct ffclock_estimate *cest
 		);
 	}
-244	AUE_NULL	STD {
+244	AUE_NULL	STD|CAPENABLED {
 		int clock_nanosleep(
 		    clockid_t clock_id,
 		    int flags,