Set max path length when paying BOLT 12 invoices.

[valentinewallace]

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

[codecov-commenter]

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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