update vplex port default value setting method

[liuxiaohuan-ghca]

What this PR does / why we need it:

Which issue this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged): fixes #

Special notes for your reviewer:

Release note:

[codecov]

Codecov Report

Merging #141 (0f4e96e) into emc_vplex_0517 (fa84903) will decrease coverage by 0.13%.
The diff coverage is 56.25%.

@@                Coverage Diff                 @@
##           emc_vplex_0517     #141      +/-   ##
==================================================
- Coverage           72.15%   72.01%   -0.14%     
==================================================
  Files                 141      141              
  Lines               11785    12080     +295     
  Branches             1381     1425      +44     
==================================================
+ Hits                 8503     8700     +197     
- Misses               2825     2896      +71     
- Partials              457      484      +27     

Impacted Files	Coverage Δ
delfin/drivers/dell_emc/vplex/vplex_stor.py	80.77% <56.25%> (-1.19%)	⬇️
delfin/drivers/dell_emc/unity/rest_handler.py	50.00% <0.00%> (-4.96%)	⬇️
delfin/drivers/dell_emc/unity/unity.py	76.61% <0.00%> (-3.87%)	⬇️