Add include files for prototypes

Include the header with prototypes in the file that provides definitions
as well, to catch any mismatch between prototype and definition.

Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Closes #10470

module/zcommon/zfs_prop.c

@@ -857,6 +857,7 @@ zfs_prop_valid_keylocation(const char *str, boolean_t encrypted)
 
 
 #ifndef _KERNEL
+#include <libzfs.h>
 
 /*
  * Returns a string describing the set of acceptable values for the given

module/zcommon/zpool_prop.c

@@ -235,6 +235,7 @@ zpool_prop_random_value(zpool_prop_t prop, uint64_t seed)
 }
 
 #ifndef _KERNEL
+#include <libzfs.h>
 
 const char *
 zpool_prop_values(zpool_prop_t prop)