kea: fix BOOST_STATIC_ASSERT use in src/lib/dns/rdataclass.cc

kea: fix BOOST_STATIC_ASSERT use in src/lib/dns/rdataclass.cc

Snapshot builds for i386_pentium-mmx (and presumably every other
target now that Boost 1.91 has been bumped in the feed) fail with::

  src/lib/dns/rdataclass.cc:1401:5: error: 'BOOST_STATIC_ASSERT'
      was not declared in this scope; did you mean
      'BOOST_HAS_STATIC_ASSERT'?
  1401 |     BOOST_STATIC_ASSERT(sizeof(numdata_) ==

``BOOST_STATIC_ASSERT`` lives in ``<boost/static_assert.hpp>``. In
earlier Boost releases it was reachable through any number of
transitive includes pulled in by Kea's other DNS headers; in 1.91
those transitive paths have been pruned, so call sites must include
the declaring header explicitly. ``050-boost-static-assert.patch``
already does this for ``src/lib/log/logger_level_impl.cc``;
``src/lib/dns/rdataclass.cc`` uses the same macro at SOA::getMinimum()
to size-check ``numdata_`` and was missed.

Extend the existing patch with the matching include in rdataclass.cc.
Same fix shape as the earlier hunk; no behavioural change.

Build log:
https://downloads.openwrt.org/snapshots/faillogs/i386_pentium-mmx/packages/kea/

Signed-off-by: Alexandru Ardelean <redacted>