libdlog: reduce pipe size 1 MB → 64 kB

libdlog: reduce pipe size 1 MB → 64 kB

It seems that the amount of memory allocated specifically to pipes
can be limited and on most targets it seems to be set to 16k pages,
that is, 64 MB raw memory. Pipes are currently very aggressively
sized which burns through this limit easily. 64 kB is still quite
a lot and should not cause any problems to prolific loggers while
heavily culling memory wastage.

Change-Id: I5465de849a279e23ca0d6bae34bceddd6136db16
Signed-off-by: Michal Bloch <m.bloch@samsung.com>