[master][dualtor] Fix config_db.json path for config-reload

[vaibhavhd]

What I did

Fix the path to config_db.json in config-reload for dual-tor device.

202012 PR: #2142

Related PR: #1465

Presently, there exists a typo in config_db.json filename that is sent as an argument to filter_fdb_entries. This causes failure during config reload:

Apr 27 01:35:26.990670 str2-7050cx3-acs-10 ERR filter_fdb_entries:
	Got an exception file '/etc/sonic/configdb.json' does not exist:
	Traceback: Traceback (most recent call last):
	#012  File "/usr/local/lib/python3.7/dist-packages/fdbutil/filter_fdb_entries.py", line 146, in main
	#012  file_exists_or_raise(config_db_filename)
	#012  File "/usr/local/lib/python3.7/dist-packages/fdbutil/filter_fdb_entries.py", line 126, in file_exists_or_raise
	#012  raise Exception("file '{0}' does not exist".format(filename))
	#012  Exception: file '/etc/sonic/configdb.json' does not exist

How I did it

Fix the typo.

How to verify it

Config reload does not throw errors any more in the syslog.

Previous command output (if the output of a command-line utility has changed)

New command output (if the output of a command-line utility has changed)

[vaibhavhd]

/Azp run

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