fix clang build with certain toolchain

[amosbird]

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work around an old kernel header bug. Or else

/home/amos/git/chorigin/dbms/src/Common/TaskStatsInfoGetter.cpp:131:14: error: comparison of integers of different signs: 'ssize_t' (aka 'long') and 'unsigned long' [-Werror,-Wsign-compare]
        if (!NLMSG_OK((&header), bytes_received))
             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/amos/gentoo/usr/include/linux/netlink.h:97:34: note: expanded from macro 'NLMSG_OK'
#define NLMSG_OK(nlh,len) ((len) >= sizeof(struct nlmsghdr) && \
                            ~~~  ^  ~~~~~~~~~~~~~~~~~~~~~~~
1 error generated.