Enforce segwit inputs for all "safe" funding transactions

[TheBlueMatt]

8403755 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.

[codecov]

Codecov Report

Attention: Patch coverage is 33.33333% with 6 lines in your changes missing coverage. Please review.

Project coverage is 89.73%. Comparing base (3733103) to head (55686b9).
Report is 2 commits behind head on main.

Files	Patch %	Lines
lightning/src/ln/channelmanager.rs	33.33%	5 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3199      +/-   ##
==========================================
+ Coverage   89.71%   89.73%   +0.01%     
==========================================
  Files         121      121              
  Lines      101074   101072       -2     
  Branches   101074   101072       -2     
==========================================
+ Hits        90680    90692      +12     
+ Misses       7701     7690      -11     
+ Partials     2693     2690       -3     

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[tnull]

LGTM

Going to land this as it's a simple move that also checks the the witness data for the funding_transaction_generated call path but not for the unsafe case, which was the goal of the change in the original PR (cc @jbesraa).