Check too many tx outputs upfront when verifying funding tx

[benthecarman]

Before you would need to iterate through all 2^16 outputs before throwing this error, thus wasting a lot of time. Moved so this check is just done upfront.

[codecov-commenter]

Codecov Report

Patch coverage: 33.33% and project coverage change: -0.54 ⚠️

Comparison is base (818dbdf) 91.50% compared to head (fcd1127) 90.96%.

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Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2278      +/-   ##
==========================================
- Coverage   91.50%   90.96%   -0.54%     
==========================================
  Files         104      104              
  Lines       52087    52656     +569     
  Branches    52087    52656     +569     
==========================================
+ Hits        47660    47900     +240     
- Misses       4427     4756     +329     

Impacted Files	Coverage Δ
lightning/src/ln/channelmanager.rs	87.23% <33.33%> (+<0.01%)	⬆️

... and 13 files with indirect coverage changes

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