Moar tests, fixed wrongly named vbles, minor bugs.

include/grpc/compression.h

src/core/channel/compress_filter.c

src/core/compression/algorithm.c

src/core/surface/call.c

src/core/surface/channel.c

test/core/compression/message_compress_test.c

test/core/end2end/tests/request_with_compressed_payload.c