set larger range to get probes evnet for test_usdt2.py

I test test_usdt2.py on aarch64 with kernel-5.9-rc5,
gcc-9.2.1 and glibc2.32.
with the current range of 3, always get failure:
======================================================================
FAIL: test_attach1 (__main__.TestUDST)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "test_usdt2.py", line 170, in test_attach1
    self.assertTrue(self.evt_st_6 == 1)
AssertionError: False is not true

----------------------------------------------------------------------
Ran 1 test in 1.068s

FAILED (failures=1)

Signed-off-by: Chunmei Xu <[email protected]>

tests/python/test_usdt2.py

@@ -149,7 +149,7 @@ def print_event6(cpu, data, size):
  b["event6"].open_perf_buffer(print_event6)
 
  # three iterations to make sure we get some probes and have time to process them
- for i in range(3):
+ for i in range(5):
  b.perf_buffer_poll()
 
  # note that event1 and event4 do not really fire, so their state should be 0