res_stasis_snoop: Spying on a single direction continually increases CPU

res_stasis_snoop: Spying on a single direction continually increases CPU

Creating a snoop channel in ARI and spying only on a single direction (in or
out) results in CPU utilization continually increasing until the CPU is fully
consumed. This occurs because frames are being put in the opposing direction's
slin factory queue, but not being removed.

Fixed the problem by always reading and disposing of frames from the opposite
queue of the direction selected.

ASTERISK-24938 #closes

Change-Id: I935bfd15f1db958f364d9d6b3b45582c0113dd60