Double inclusion of errno.h

[burkaykinik]

In the common_user_bpf_xdp.c, errno.h is included twice.

See the following lines:
https://github.com/xdp-project/xdp-tutorial/blob/61e24d3344b43a87297a31cfa6e83171931f2f00/common/common_user_bpf_xdp.c#L5C1-L6C19

[burkaykinik]

The same goes for bpf/libbpf.h. It is included twice