DRY redundant calls to $candidate.htlc_minimum_msat() in routing

While LLVM should inline and elide the redundant calls, because the
router is rather large LLVM can decide against inlining in some
cases where it would be an nice win.

Thus, its worth DRY'ing the redundant calls explicitly.

Author: TheBlueMatt

lightning/src/routing/router.rs

@@ -2202,14 +2202,15 @@ where L::Target: Logger {
 						// Can't overflow due to how the values were computed right above.
 						None => unreachable!(),
 					};
+					let htlc_minimum_msat = $candidate.htlc_minimum_msat();
 					#[allow(unused_comparisons)] // $next_hops_path_htlc_minimum_msat is 0 in some calls so rustc complains
-					let over_path_minimum_msat = amount_to_transfer_over_msat >= $candidate.htlc_minimum_msat() &&
+					let over_path_minimum_msat = amount_to_transfer_over_msat >= htlc_minimum_msat &&
 						amount_to_transfer_over_msat >= $next_hops_path_htlc_minimum_msat;
 
 					#[allow(unused_comparisons)] // $next_hops_path_htlc_minimum_msat is 0 in some calls so rustc complains
 					let may_overpay_to_meet_path_minimum_msat =
-						((amount_to_transfer_over_msat < $candidate.htlc_minimum_msat() &&
-						  recommended_value_msat >= $candidate.htlc_minimum_msat()) ||
+						((amount_to_transfer_over_msat < htlc_minimum_msat &&
+						  recommended_value_msat >= htlc_minimum_msat) ||
 						 (amount_to_transfer_over_msat < $next_hops_path_htlc_minimum_msat &&
 						  recommended_value_msat >= $next_hops_path_htlc_minimum_msat));