Allow creation of valid `CSubNet` objects of non-IP networks and only
match the single address they were created from (like /32 for IPv4 or
/128 for IPv6).
This fixes a deficiency in `CConnman::DisconnectNode(const CNetAddr& addr)`
and in `BanMan` which assume that creating a subnet from any address
using the `CSubNet(CNetAddr)` constructor would later match that address
only. Before this change a non-IP subnet would be invalid and would not
match any address.
Github-Pull: #20852
Rebased-From: 94d335da7f