Bump external/bpf_conformance from `e80df99` to `b1b1c21` #149

Job	Run time
build_windows (Debug, tests)	35m 26s
build_ubuntu (Debug, tests)	25m 47s
build_windows (Debug, library)	5m 5s
build_ubuntu (Debug, library)	1m 25s
build_windows (Release, tests)	9m 19s
build_ubuntu (Release, tests)	5m 39s
build_windows (Release, library)	5m 35s
build_ubuntu (Release, library)	1m 39s
	1h 29m 55s

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