nimble/test: Fix expected error for key size lower than minimum
nimble/test: Fix expected error for key size lower than minimum

For key size lower than minimum, an "Encryption Key Size" error shall
be returned, not "Invalid Parameters".

X-Original-Commit: c3f9aa1968a483183de60ad9a8bf43545fa0c36a

apache/mynewt-nimble,apache/mynewt-nimble,apache/mynewt-nimble,apache/mynewt-nimble,apache/mynewt-nimble