fix build against libstdc++ 12

[jvgutierrez]

While attempting to compile katran on Debian Bullseye and Bookworm I've realized that it compiled as expected on Bullseye with clang-13 but failed on Bookworm with the same compiler issuing the following error:

/tmp/fbcode_builder_getdeps-ZrootZkatranZbuildZfbcode_builder-root/repos/github.com-facebookincubator-katran.git/katran/lib/BpfLoader.cpp:46:25:
 error: implicit instantiation of undefined template 'std::array<char, 128>'
 std::array<char, 128> buf{};

Debugging the issue with clang++ -H I've noticed that BpfLoader.h:21: #include <unordered_map>
implicitly includes array when using libstdc++ 10:

.. /usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/unordered_map
... /usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/bits/hashtable.h
.... /usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/bits/hashtable_policy.h
..... /usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/tuple
...... /usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/array
...... /usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/bits/uses_allocator.h
...... /usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/bits/invoke.h
..... /usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/limits
... /usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/bits/unordered_map.h

but this doesn't happen with libstdc++ 12:

.. /usr/bin/../lib/gcc/x86_64-linux-gnu/12/../../../../include/c++/12/unordered_map
... /usr/bin/../lib/gcc/x86_64-linux-gnu/12/../../../../include/c++/12/bits/hashtable.h
.... /usr/bin/../lib/gcc/x86_64-linux-gnu/12/../../../../include/c++/12/bits/hashtable_policy.h
..... /usr/bin/../lib/gcc/x86_64-linux-gnu/12/../../../../include/c++/12/tuple
...... /usr/bin/../lib/gcc/x86_64-linux-gnu/12/../../../../include/c++/12/bits/uses_allocator.h
.... /usr/bin/../lib/gcc/x86_64-linux-gnu/12/../../../../include/c++/12/bits/enable_special_members.h
... /usr/bin/../lib/gcc/x86_64-linux-gnu/12/../../../../include/c++/12/bits/unordered_map.h

Adding a explicit #include <array> fixes the error

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