Increase memory threshold for test_tunnel_memory_leak to reduce flakiness (sonic-net#17040)

Description of PR
Summary:
Fixes # (issue)
test_tunnel_memory_leak is flaky, sometimes it failed:
Failed: Test failed because there is memory leak on dut

Based on the calculation:

21/11/2024 20:15:33 test_tunnel_memory_leak.test_tunnel_memo L0167 INFO   | tunnel_packet_handler.py original MEM USAGE:61.8046875

21/11/2024 20:24:33 test_tunnel_memory_leak._check_memory    L0102 ERROR  | tunnel_packet_handler.py MEM usage exceeds the threshold. current usage:64.3671875, target usage: 63.658828125
64.3671875/61.8046875 - 1= 0.041461
actual increased percentage is more than 4%.

The current percentage is 3%.
Confirmed with tunnel feature owner, it's safe to increase it to 5% to reduce the flakiness.

Author: ZhaohuiS

tests/dualtor/test_tunnel_memory_leak.py

@@ -31,8 +31,8 @@
 
 PACKET_COUNT = 1000
 # It's normal to see the mem usage increased a little bit
-# set threshold buffer to 0.03%
-MEM_THRESHOLD_BUFFER = 0.03
+# set threshold buffer to 5%
+MEM_THRESHOLD_BUFFER = 0.05
 
 
 def validate_neighbor_entry_exist(duthost, neighbor_addr):