- see comment in lnaddr.py
- Previously we used feature bit 50/51 for trampoline.
The spec subsequently defined fbit 50/51 as option_zeroconf, which
requires fbit 46/47 (option_scid_alias) to also be set.
We moved the non-standard trampoline fbit to a different int.
However, old wallets might have old invoices saved that set fbit 50/51
for trampoline, and those would not have the dependent bit set.
Invoices are parsed at wallet-open, so if the parser ran these checks,
those wallets could not be opened.
- note: we could potentially also run lnaddr.validate_and_compare_features
when saving new invoices into the wallet but this is not done here
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