Various fix for test_dip_sip

[wangxin]

Description of PR

Summary:
Fixes # (issue)

Type of change

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

Approach

What is the motivation for this PR?

The test_dip_sip script has some minor issues need to be fixed.

How did you do it?

Changes:

• Change topology mark from "any" to "t0" and "t1"
• Remove unused variables
• Check topology type rather than name
• Fix typo in log message
• Remove calling the Ansible setup module, use minigraph to get
  router and host IP addresses
• Use router mac from duthost.facts['router_mac']
• Simplify the code for getting src and dst port ids

How did you verify/test it?

sonicbld@88d79e903dc1:~/code/sonic-mgmt2/tests$ py.test --inventory ../ansible/inventory --host-pattern sonic-switch --testbed sonic-testbed --testbed_file ../ansible/testbed.csv ipfwd/test_dip_sip.py                                       
=========================================================================================================== test session starts ===========================================================================================================
platform linux2 -- Python 2.7.12, pytest-4.6.5, py-1.8.1, pluggy-0.13.1
ansible: 2.8.12
rootdir: /var/sonicbld/code/sonic-mgmt2/tests, inifile: pytest.ini
plugins: forked-1.1.3, xdist-1.28.0, ansible-2.2.2, repeat-0.8.0
collected 1 item                                                                                                                                                                                                                          

ipfwd/test_dip_sip.py .                                                                                                                                                                                                             [100%]

======================================================================================================== 1 passed in 59.37 seconds ========================================================================================================

Any platform specific information?

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

Documentation

[noaOrMlnx]

LGTM

[daall]

Suggested change

	pytest.mark.topology('t0', "t1")
	pytest.mark.topology("t0", "t1")

For consistency. :)

[wangxin]

Sure, updated.