samba: fix paths in sysv initscript

The sysv initscript provided by samba assumes smbd and nmbd are
installed in /opt/samba/bin/. In our case both binaries are installed to
/usr/sbin/ by default. Therefore fix these paths.

Furthermore fix the log and config directory as well as the name of the
initscript in its usage text.

Signed-off-by: Richard Leitner <richard.leitner@skidata.com>
Signed-off-by: Joe MacDonald <joe_macdonald@mentor.com>