Enforce segwit inputs for all "safe" funding transactions

Enforce segwit inputs for all "safe" funding transactions

8403755a2a524beb9f6c8951f51dd60f7c54c912 introduced a separate path
for funding a channel without a full funding transaction, relying
on users to manually broadcast the funding tx. One of the major
things that makes this path less safe is that for other paths we're
supposed to validate that all inputs have witnesses, making the
funding transaction (likely) txid-non-malleable.

However, in one of several rewrites of that commit the funding tx
tests ended up getting elided in some call paths, which is fixed
here.