p2p: Avoid InitError when downgrading peers.dat

fixes #24188
When downgrading, a peers.dat with a future version that has a minimum
required version larger than the downgraded version would cause an InitError.

This commit changes this behavior to overwrite the existing peers.dat with
a new empty one, while creating a backup in peers.dat.bak.

src/addrman.h

@@ -17,6 +17,12 @@
 #include <utility>
 #include <vector>
 
+class InvalidAddrManVersionError : public std::ios_base::failure
+{
+public:
+    InvalidAddrManVersionError(std::string msg) : std::ios_base::failure(msg) { }
+};
+
 class AddrManImpl;
 
 /** Default for -checkaddrman */