audiohook.c: Difference in read/write rates caused continuous buffer resets

audiohook.c: Difference in read/write rates caused continuous buffer resets

Currently, everytime a sample rate change occurs (on read or write) the
associated factory buffers are reset. If the requested sample rate on a
read differed from that of a write then the buffers are continually reset
on every read and write. This has the side effect of emptying the buffer,
thus there being no data to read and then write to a file in the case of
call recording.

This patch fixes it so that an audiohook_list's rate always maintains the
maximum sample rate among hooks and formats. Audiohook sample rates are
only overwritten by this value when slin native compatibility is turned on.
Also, the audiohook sample rate can only overwrite the list's sample rate
when its rate is greater than that of the list or if compatibility is
turned off. This keeps the rate from constantly switching/resetting.

ASTERISK-24944 #close
Reported by: Ronald Raikes

Change-Id: Idab4dfef068a7922c09cc631dda27bc920a6c76f