[FRR]Adding fix for memory leak seen with BGP community (#18272)

Why I did it
Porting fix for FRRouting/frr#15459

Adding patch for PR FRRouting/frr#15466

Work item tracking
Microsoft ADO (number only):
How I did it
Ported the fix FRRouting/frr#15466 to 8.5.1

How to verify it
Running the test_stress_route and ensure no memory leak

Author: dgsudharsan