TEST: Add test for 0 blocks for UNMAP and fix num_blocks which was off by one

across the testsuite

test-tool/iscsi-test-cu.h

@@ -68,6 +68,7 @@ void test_readcapacity16_simple(void);
 void test_readcapacity16_alloclen(void);
 
 void test_unmap_simple(void);
+void test_unmap_0blocks(void);
 
 void test_verify10_simple(void);
 void test_verify10_beyond_eol(void);