FreeSWITCH: Fix format string error in witch_core_session_thread_pool_worker().

FreeSWITCH: Fix format string error in witch_core_session_thread_pool_worker().

Fixes:
    cc1: warnings being treated as errors
    src/switch_core_session.c: In function 'switch_core_session_thread_pool_worker':
    src/switch_core_session.c:1478: warning: format '%ld' expects type 'long int', but argument 9 has type 'switch_size_t'
    src/switch_core_session.c:1483: warning: format '%ld' expects type 'long int', but argument 9 has type 'switch_size_t'
    gmake[2]: *** [libfreeswitch_la-switch_core_session.lo] Error 1

Signed-off-by: Stefan Knoblich <stkn@openisdn.net>