player: eventfd leak on GMainContext
valgrind unit test with --track-fds=yes
option reported that there is eventfd leak.
$GST_CHECKS=test_create_and_free make libs/player.valgrind
==10668== FILE DESCRIPTORS: 5 open at exit.
==10668== Open file descriptor 5:
==10668== at 0x5CA0A87: eventfd (syscall-template.S:78)
==10668== by 0x58FABA6: g_wakeup_new (gwakeup.c:146)
==10668== by 0x589F6AE: g_main_context_new (gmain.c:658)
==10668== by 0x589F755: g_main_context_default (gmain.c:694)
==10668== by 0x589F80B: g_main_context_push_thread_default (gmain.c:783)
==10668== by 0x4E4B9E2: gst_player_main (gstplayer.c:2882)
==10668== by 0x58D4197: g_thread_proxy (gthread.c:784)
==10668== by 0x6C726DA: start_thread (pthread_create.c:463)
==10668== by 0x5CA088E: clone (clone.S:95)