The driver was printing out a lot of information upon failure, which
does not have to be interested for the user.
Changing logging level required to rebuild driver with proper flags. The
proper sysctl was added, so the level now can be changed dynamically
using bitmask.

Levels of printouts were adjusted to keep on mind end user instead of
debugging purposes.

More verbose messages were added to align the driver with the Linux.

Fix building error introduced by the r325506 by casting csum_flags to
uint64_t.