[iccpd]enhance for add_to_syncd

[pettershao-ragilenetworks]

Why I did it

Enhance for add_to_syncd not modified after add_mac_to_chip, if not enhance, may cause fdb removed in iccpd, but still exist in app_db and asic_db. check below code:

if (mac_info->add_to_syncd)
{
    del_mac_from_chip(mac_info);
}

How I did it

How to verify it

Which release branch to backport (provide reason below if selected)

• 201811
• 201911
• 202006
• 202012
• 202106

Description for the changelog

A picture of a cute animal (not mandatory but encouraged)

[pettershao-ragilenetworks]

@Praveen-Brcm help review this, thanks!

[pettershao-ragilenetworks]

@Praveen-Brcm help review this, thanks!

[pettershao-ragilenetworks]

@gechiang @qiluo-msft help forward this, thanks!

[gechiang]

@pettershao-ragilenetworks Can you also include test cases to ensure new changes are unit tested?
Issue such as this slipped because these were not properly tested (missing unit test code) when the code was first developed.
So going forward our request is to at the minimum to add unit test case that should exercise the portion of the code that you are modifying. once this is included, alert me to review. Thanks!