Improve DFS file opens

[jborean93]

Ensure that opening a file on a DFS marked share contains the
SMB2_FLAGS_DFS_OPERATIONS flag and create filename contains the DFS path
to parse and not just the tree relative path.

Related #170.

[codecov]

Codecov Report

Merging #190 (53f2e33) into master (bc401b7) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #190   +/-   ##
=======================================
  Coverage   99.09%   99.09%           
=======================================
  Files          24       24           
  Lines        5069     5076    +7     
=======================================
+ Hits         5023     5030    +7     
  Misses         46       46           

Flag	Coverage Δ
macOS	68.20% <25.00%> (-0.06%)	⬇️
py3.10	99.07% <100.00%> (+<0.01%)	⬆️
py3.7	99.07% <100.00%> (+<0.01%)	⬆️
py3.8	99.07% <100.00%> (+<0.01%)	⬆️
py3.9	99.09% <100.00%> (+<0.01%)	⬆️
ubuntu	96.78% <100.00%> (+<0.01%)	⬆️
windows	99.01% <100.00%> (+<0.01%)	⬆️
x64	99.09% <100.00%> (+<0.01%)	⬆️
x86	99.01% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/smbclient/_io.py	99.03% <100.00%> (+<0.01%)	⬆️
src/smbclient/_os.py	98.48% <100.00%> (ø)
src/smbprotocol/connection.py	99.84% <100.00%> (+<0.01%)	⬆️

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