tests/qtest/migration: Re-enable postcopy tests

tests/qtest/migration: Re-enable postcopy tests

Postcopy tests have been inadvertently disabled since commit
124a3c58b8 ("tests/qtest/migration: Move ufd_version_check to
utils"). That commit moved the ufd_version_check() function to another
file but failed to make sense of the ifdefs and includes:

The <sys/syscall> include was incorrectly dropped. It is needed to
pull in <asm/unistd.h> for __NR_userfaultfd.

The <sys/ioctl.h> was moved under the wrong ifdef.

Fixes: 124a3c58b8 ("tests/qtest/migration: Move ufd_version_check to utils")
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
Message-Id: <20241218192223.10551-2-farosas@suse.de>