FreeBSD: Don't require zeroing new locks before init

This has not shown to be of use enough to justify the inconvenience.

Reviewed-by: Matt Macy <mmacy@FreeBSD.org>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Allan Jude <allanjude@freebsd.org>
Signed-off-by: Ryan Moeller <ryan@iXsystems.com>
Closes #10449

include/os/freebsd/spl/sys/mutex.h

@@ -39,7 +39,7 @@ typedef struct sx	kmutex_t;
 #include <sys/sx.h>
 
 typedef enum {
-	MUTEX_DEFAULT = 6	/* kernel default mutex */
+	MUTEX_DEFAULT = 0	/* kernel default mutex */
 } kmutex_type_t;
 
 #define	MUTEX_HELD(x)		(mutex_owned(x))
@@ -53,9 +53,7 @@ typedef enum {
 
 #define	mutex_init(lock, desc, type, arg)	do {			\
 	const char *_name;						\
-	ASSERT((type) == 0 || (type) == MUTEX_DEFAULT);			\
-	KASSERT(((lock)->lock_object.lo_flags & LO_ALLMASK) !=		\
-	    LO_EXPECTED, ("lock %s already initialized", #lock));	\
+	ASSERT((type) == MUTEX_DEFAULT);				\
 	for (_name = #lock; *_name != '\0'; _name++) {			\
 		if (*_name >= 'a' && *_name <= 'z')			\
 			break;						\