bitbake: event/msg: Add primitive server side UI log record filtering

bitbake: event/msg: Add primitive server side UI log record filtering

Currently one of the bigger bottlenecks in bitbake is passing all the
log messages over IPC to the UI. This is worthwhile if the UI is going
to use them, pointless otherwise. The memory resident bitbake suffers
from this performance issue particularly badly.

This patch filters the log events on the server side with the global
log levels and hence reduces the traffic. This speeds up parsing
(18.5s down to 17s) and bitbake general command overhead is reduced
(7.3s for a NOP to 6.2s).

What isn't added here is general event filtering or the ability to
change the log levels once set. Provision is made for adding this
in a follow up patch though.

(Bitbake rev: 1bf0e88f57ba0bca62532e81d0d62cf88e2abcbb)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>