osdep: Less restrictive F_SEFL in qemu_dup_flags()

qemu_dup_flags() currently limits the flags that can be set on the
fcntl() F_SETFL call to those that we currently know can be set with
fcntl() F_SETFL.  The problem with this is that it will prevent use
of new flags in the future without a code update.

This patch relaxes the checking and lets fcntl() determine the flags
it can set.

Signed-off-by: Corey Bryant <coreyb@linux.vnet.ibm.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
