source outcomes are incorrectly encoded in attach response sent to a producer

[gemmellr]

When a producer tries to attach a sending link with source outcomes set, the attach response sent by the broker incorrectly encodes the source outcomes as a list of symbols instead of an array of symbols, causing the process to fail.

In contrast, when a consumer attaches a receiving link with source outcomes set the attach response from the broker correctly contains the required array encoding.

This is seen using broker version 3.6.5