Remove errno assignments

If we want to report something libsmack specific, then we should
have our own error codes. By using errno values to report libsmack
specific error condition we almost zero their value. By removing
these assignment you can resolved from a changed errno value that
a system call failed.

This patch does not break API contract as use of errno values is
undefined in the API documentation.
(cherry picked from commit 1edba541de63b088a60d89e4a0433bf9149c4b13)