log: do not drop debug logs at compile time

log: do not drop debug logs at compile time

Today, all logs whose level is lower than INFO are dropped at
compile-time. This prevents from enabling debug logs at runtime using
--log-level=8.

The rationale was to remove debug logs from the data path at
compile-time, avoiding a test at run-time.

This patch changes the behavior of RTE_LOG() to avoid the compile-time
optimization, and introduces the RTE_LOG_DP() macro that has the same
behavior than the previous RTE_LOG(), for the rare cases where debug
logs are in the data path.

So it is now possible to enable debug logs at run-time by just
specifying --log-level=8. Some drivers still have special compile-time
options to enable more debug log. Maintainers may consider to
remove/reduce them.

Signed-off-by: Olivier Matz <olivier.matz@6wind.com>