libubox: update to the latest version

libubox: update to the latest version

870acee325fe tests: cram: test_base64: fix failing tests
4d8995e91d56 tests: cram: test_base64: really fix failing tests
551d75b5662c libubox: tests: add more blobmsg/json test cases
a0dbcf8b8f96 tests: add blob-buffer overflow test
b36a3a90098d blob: fix exceeding maximum buffer length
b8abed749423 utils.h: add fallthrough macro
b14c4688612c json_script: fix unannotated fall-through warning

Signed-off-by: Felix Fietkau <nbd@nbd.name>
(cherry picked from commit 04d21604fd72f337c8a0410d13b3d878914b7e7e)