backport PR9962 https://github.com/bitcoin/bitcoin/pull/9962/files
9ea2490 [trival] Fix typo introduced into rpc/protocol.h in commit 338bf06 (practicalswift)
Tree-SHA512: bfa60dc9f40db867b09e60dbe803db79c86ff939048c91e551c0794a91428bde3aa42c4aabf915c640cd15565005608da10dae051942e806fdf5d28e9704d765