cleaning up tabs and trailing whitespace

Strictly whitespace changes - there were a bunch of tab characters littered throughout and some trailing spaces.

$ git show 84a21ec6720ec085f56feb5f81b61d54605cdaee -w --pretty=oneline
84a21ec6720ec085f56feb5f81b61d54605cdaee remove tabs and use soft whitespaces
$ 
As are these. I think this file might be screwed up because the top level `module Net::SNMP` is indented wrong.