fix fdb test on sonic kvm image

[lguohan]

Do not check total mac as there could be more macs from neighbors
Result unstable tests

Signed-off-by: Guohan Lu gulv@microsoft.com

Description of PR

Summary:
Fixes # (issue)

Type of change

• [] Bug fix
• [] Testbed and Framework(new/improvement)
• Test case(new/improvement)

Approach

How did you do it?

Do not check total mac as there could be more macs from neighbors
Result unstable tests

How did you verify/test it?

johnar@2cd47dfe744e:/data/sonic-mgmt/tests$ py.test --inventory veos.vtb --host-pattern all --user admin --show-capture stdout --testbed vms-kvm-t0 --testbed_file vtestbed.csv fdb/test_fdb.py   | tee abc.txt
============================= test session starts ==============================
platform linux2 -- Python 2.7.12, pytest-4.6.6, py-1.8.0, pluggy-0.13.0
ansible: 2.8.7
rootdir: /data/sonic-mgmt/tests, inifile: pytest.ini
plugins: ansible-2.2.2
collected 1 item

fdb/test_fdb.py .                                                        [100%]

========================== 1 passed in 230.50 seconds ==========================

Any platform specific information?

Supported testbed topology if it's a new test case?

Documentation