nlbwmon: update to latest Git HEAD

nlbwmon: update to latest Git HEAD

4574e6e nfnetlink: prevent tight retry loops
163a211 client: fix commit error information
21290db nlbwmon: merge existing data
abe701d database: do not overwrite unexpectedly preexisting databases
ef3fa58 socket: handle EAGAIN on send()

Ref: https://github.com/jow-/nlbwmon/issues/23
Ref: https://github.com/jow-/nlbwmon/issues/26
Ref: https://github.com/jow-/nlbwmon/issues/30
Signed-off-by: Jo-Philipp Wich <jo@mein.io>
(cherry picked from commit c528e01f4cb5112cbd26b973400ad424280a61e1)