Correct syslog use for priority codes

[dgraziotin]

Currently, only LOG_INFO is used.
See http://ftp.gnu.org/old-gnu/Manuals/glibc-2.2.3/html_chapter/libc_18.html

[Yamakaky]

As you are here, you could use LOG_DEBUG in the main loop, mbpfan.c:540-560.