lib/reduce: change and move the max IOVEC define for reduce

Changed to 17 from 32 per conversation with Jim and moved to
header file so it can be shared with the vbdev module.

Change-Id: Ic516b6466bf21d21d8073e9180deaa9929c6b742
Signed-off-by: paul luse <paul.e.luse@intel.com>
Reviewed-on: https://review.gerrithub.io/c/spdk/spdk/+/463368
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Reviewed-by: Shuhei Matsumoto <shuhei.matsumoto.xt@hitachi.com>
Reviewed-by: Jim Harris <james.r.harris@intel.com>
Reviewed-by: Broadcom SPDK FC-NVMe CI <spdk-ci.pdl@broadcom.com>

include/spdk/reduce.h

@@ -40,6 +40,8 @@
 
 #include "spdk/uuid.h"
 
+#define REDUCE_MAX_IOVECS	17
+
 /**
  * Describes the parameters of an spdk_reduce_vol.
  */

lib/reduce/reduce.c

@@ -87,8 +87,6 @@ struct spdk_reduce_chunk_map {
 	uint64_t		io_unit_index[0];
 };
 
-#define REDUCE_MAX_IOVECS	32
-
 struct spdk_reduce_vol_request {
 	/**
 	 *  Scratch buffer used for uncompressed chunk.  This is used for: