Add a temporary hack that will go away with the ucred API update to bzero

the duplicated mutex before initializing it to avoid triggering the check
for init'ing an already initialized mutex.

sys/kern/kern_prot.c

@@ -1671,6 +1671,7 @@ crdup(cr)
 
 	MALLOC(newcr, struct ucred *, sizeof(*cr), M_CRED, M_WAITOK);
 	*newcr = *cr;
+	bzero(&newcr->cr_mtx, sizeof(newcr->cr_mtx));
 	mtx_init(&newcr->cr_mtx, "ucred", MTX_DEF);
 	uihold(newcr->cr_uidinfo);
 	uihold(newcr->cr_ruidinfo);