Set max path length when paying BOLT 12 invoices.

[valentinewallace]

This should've been done as part of #3026 but got overlooked.

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Codecov Report

Attention: Patch coverage is 96.87500% with 2 lines in your changes missing coverage. Please review.

Project coverage is 89.80%. Comparing base (669a459) to head (678aac0).
Report is 3 commits behind head on main.

Files	Patch %	Lines
lightning/src/ln/outbound_payment.rs	75.00%	1 Missing and 1 partial ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3156      +/-   ##
==========================================
- Coverage   89.84%   89.80%   -0.05%     
==========================================
  Files         121      121              
  Lines       99454    99526      +72     
  Branches    99454    99526      +72     
==========================================
+ Hits        89357    89381      +24     
- Misses       7498     7533      +35     
- Partials     2599     2612      +13     

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[tnull]

LGTM, one question

[valentinewallace]

Squashed in nit with this diff:

diff --git a/lightning/src/ln/outbound_payment.rs b/lightning/src/ln/outbound_payment.rs
index a9fba2c56..443a7b2c3 100644
--- a/lightning/src/ln/outbound_payment.rs
+++ b/lightning/src/ln/outbound_payment.rs
@@ -510,7 +510,7 @@ pub enum Bolt12PaymentError {
        UnexpectedInvoice,
        /// Payment for an invoice with the corresponding [`PaymentId`] was already initiated.
        DuplicateInvoice,
-       /// The [`BlindedPath`]s provided are too large and caused us to exceed the maximum onion packet
+       /// The [`BlindedPath`]s provided are too large and caused us to exceed the maximum onion hop data
        /// size of 1300 bytes.
        ///
        /// [`BlindedPath`]: crate::blinded_path::BlindedPath

[valentinewallace]

Trivial fix with a test so I'm gonna land with 1 ACK