LC15: use talloc pool for msgb and ortp library
LC15: use talloc pool for msgb and ortp library

by using a talloc pool, we avoid having to go back to the libc
malloc pool all the time.  The msgb allocations and libortp allocations
happen quite frequently during processing and show up as one of the
high priority items in osmo-bts profiles on sysmoBTS with 14 concurrent
TCH/H calls (highest load scenario).

talloc still consumes significant CPU, this is mostly due to the
zero-initialization of all the associated buffers.  Strictly speaking
we shouldn't need this, but any change there would require lots of
testing, as there might be hidden assumptions in the code?

In some percentage of cases, talloc still seems to fall back on malloc
for msgb allocations, which is currently a bit of a mystery.  The pools
certainly are large enough, talloc_reprt() rarely reports more than a
few tens of kilobytes used by the msgb pool.

From 2ecbf871301cdc36c0212dd7526fc94ffa4597d1

osmocom/osmo-bts,osmocom/osmo-bts,osmocom/osmo-bts