Fix disable channel and private channel send payment issue

[chenyukang]

1: Fixes #499, disable will respect direction, for scenario a -> b -> c, if b disable b -> c, c can send payment with c -> b -> a.

2: Fix a payment issue in channel forwarding.

[gpBlockchain]

LGTM

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 60.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 50.58%. Comparing base (f624685) to head (e7bb887).

Files with missing lines	Patch %	Lines
src/fiber/channel.rs	60.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #502      +/-   ##
===========================================
+ Coverage    50.56%   50.58%   +0.01%     
===========================================
  Files           49       49              
  Lines        31945    31944       -1     
===========================================
+ Hits         16154    16159       +5     
+ Misses       15791    15785       -6     

Flag	Coverage Δ
unittests	50.58% <60.00%> (+0.01%)	⬆️

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