log: use smaller buffer for ConcreteEntry

log: use smaller buffer for ConcreteEntry

This brings down the static size of the memory used by the logging infrastructure:

    If we used 1024, we'd have 1088*10000 = 10880000 = 10MB in use by the ring
    buffer and 2*1088*100 = 2*108800 = 2*106KB for the m_new and m_flush
    vectors.

In my testing, 1024 covers most log entries.

Note, I've kept 4096 for the StackStringStream via MutableEntry as these are
already allocated on the heap and cached in a thread local vector. Generally
there should only be about a dozen of these allocated so it's worth keeping a
larger buffer.

Signed-off-by: Patrick Donnelly <pdonnell@redhat.com>