lib/iscsi: add a comment for iscsi_parse_params()

When param len > 0, param data must not be NULL.
So we add a comment to make it clearer.

Change-Id: I053c3e45ddb8fa23fb67ce899d32dadd8e286946
Signed-off-by: wanghailiangx <hailiangx.e.wang@intel.com>
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/6618
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>

lib/iscsi/param.c

@@ -306,6 +306,8 @@ iscsi_parse_param(struct iscsi_param **params, const uint8_t *data, uint32_t dat
  *
  * \param data "KEY=VAL<NUL>KEY=VAL<NUL>..."
  * \param len length of data in bytes
+ *
+ * Data must point to a valid pointer if len > 0.
  */
 int
 iscsi_parse_params(struct iscsi_param **params, const uint8_t *data,