fix: return error when AddChannel fails

[ulbqb]

Description

AddChannel doesn't return an error if adding a channel fails. I fixed AddChannel to return an error on failure.

[codecov]

Codecov Report

Merging #500 (dfcf497) into main (0681636) will increase coverage by 0.04%.
The diff coverage is 76.92%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #500      +/-   ##
==========================================
+ Coverage   65.44%   65.49%   +0.04%     
==========================================
  Files         278      278              
  Lines       37936    37972      +36     
==========================================
+ Hits        24828    24868      +40     
+ Misses      11305    11294      -11     
- Partials     1803     1810       +7     

Impacted Files	Coverage Δ
p2p/node_info.go	95.12% <ø> (ø)
p2p/transport.go	82.77% <66.66%> (-0.71%)	⬇️
node/node.go	60.20% <100.00%> (+0.08%)	⬆️
mempool/reactor.go	78.57% <0.00%> (-1.10%)	⬇️
consensus/reactor.go	74.22% <0.00%> (-0.98%)	⬇️
consensus/wal.go	60.88% <0.00%> (-0.89%)	⬇️
consensus/state.go	73.50% <0.00%> (-0.35%)	⬇️
proxy/multi_app_conn.go	47.66% <0.00%> (ø)
... and 6 more