smb: apply a whole bunch of static analyzer improvements

Summary:
among other things:

- {} initialize the posix structs
- =default d/ctors where appropriate
- synced argument names between header and cpp
- no c-style casting
- while(true) instead of while(1)
- initialize class members that could previously have gone uninitialized
- no single-line-multi-variable declaration

Test Plan: builds

Reviewers: ngraham

Reviewed By: ngraham

Subscribers: kde-frameworks-devel, kfm-devel

Tags: #dolphin, #frameworks

Differential Revision: https://phabricator.kde.org/D27646