RTP: disable preemption during queueing
RTP: disable preemption during queueing

This should fix a rare crash:
LibVLC fatal error destroying mutex (16) in thread 17390 at ../../src/misc/pthread.c:188 in vlc_mutex_destroy
/home/remi/videolan/vlc/build/src/.libs/libvlccore.so.4[0xb7fff933]
/home/remi/videolan/vlc/build/src/.libs/libvlccore.so.4[0xb7fff9c8]
/home/remi/videolan/vlc/build/src/.libs/libvlccore.so.4(vlc_mutex_destroy+0x3f)[0xb7fffa39]
/home/remi/videolan/vlc/build/modules/access/rtp/.libs/librtp_plugin.so[0xb5563a41]
/home/remi/videolan/vlc/build/src/.libs/libvlccore.so.4(__module_unneed+0x29)[0xb7fe414f]
/home/remi/videolan/vlc/build/src/.libs/libvlccore.so.4[0xb7f9984e]
/home/remi/videolan/vlc/build/src/.libs/libvlccore.so.4[0xb7fa69fb]
/home/remi/videolan/vlc/build/src/.libs/libvlccore.so.4[0xb7fa6c0c]
/home/remi/videolan/vlc/build/src/.libs/libvlccore.so.4[0xb7faeef2]
/home/remi/videolan/vlc/build/src/.libs/libvlccore.so.4[0xb7feb16e]
/lib/i686/cmov/libpthread.so.0[0xb7f324b5]
/lib/i686/cmov/libc.so.6(clone+0x5e)[0xb7eaea5e]

jomanmuk/vlc-2.2,jomanmuk/vlc-2.2,krichter722/vlc,krichter722/vlc,vlc-mirror/vlc-2.1,jomanmuk/vlc-2.1,vlc-mirror/vlc-2.1,shyamalschandra/vlc,vlc-mirror/vlc,shyamalschandra/vlc,vlc-mirror/vlc-2.1,krichter722/vlc,vlc-mirror/vlc,shyamalschandra/vlc,krichter722/vlc,jomanmuk/vlc-2.2,krichter722/vlc,vlc-mirror/vlc,shyamalschandra/vlc,xkfz007/vlc,shyamalschandra/vlc,jomanmuk/vlc-2.2,jomanmuk/vlc-2.2,shyamalschandra/vlc,vlc-mirror/vlc,vlc-mirror/vlc,xkfz007/vlc,vlc-mirror/vlc-2.1,xkfz007/vlc,jomanmuk/vlc-2.2,vlc-mirror/vlc,vlc-mirror/vlc-2.1,jomanmuk/vlc-2.1,jomanmuk/vlc-2.2,xkfz007/vlc,vlc-mirror/vlc,xkfz007/vlc,jomanmuk/vlc-2.1,krichter722/vlc,krichter722/vlc,jomanmuk/vlc-2.1,xkfz007/vlc,vlc-mirror/vlc-2.1,jomanmuk/vlc-2.1,shyamalschandra/vlc,xkfz007/vlc,vlc-mirror/vlc-2.1,jomanmuk/vlc-2.1,jomanmuk/vlc-2.1