Send Init message immediately after handshake even if not initiator

[devrandom]

We were waiting for the initiator, but the spec doesn't guarantee that they will send Init first, so we might theoretically wait forever.

Also, lnprototest expects this behavior.

[codecov]

Codecov Report

Merging #900 (7113dbd) into main (affefb6) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #900   +/-   ##
=======================================
  Coverage   90.35%   90.36%           
=======================================
  Files          57       57           
  Lines       29353    29352    -1     
=======================================
+ Hits        26522    26523    +1     
+ Misses       2831     2829    -2     

Impacted Files	Coverage Δ
lightning/src/ln/peer_handler.rs	44.17% <100.00%> (-0.07%)	⬇️
lightning/src/ln/functional_tests.rs	96.85% <0.00%> (+0.03%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update affefb6...7113dbd. Read the comment docs.

[ariard]

Code Review ACK 7113dbd

I read again the BOLT init section and effectively it says :

The sending node:
  - MUST send `init` as the first Lightning message for any connection.

Without precising if the sending maps to inbound or outbound or indifferent. Even if minor, I would invite to clarify the spec on this point.