Tweak OAEP's `MAX_LABEL_LEN` constant #717

Job	Run time
nightly	1m 15s
build (1.72.0, thumbv7em-none-eabi)	23s
minimal-versions	48s
doc	44s
build (1.72.0, wasm32-unknown-unknown)	24s
build (stable, thumbv7em-none-eabi)	16s
test (1.72.0)	7m 59s
build (stable, wasm32-unknown-unknown)	18s
test (stable)	7m 4s
	19m 11s

Provide feedback