[BUG] KernelSymbolTable exposed to owner value vulnerability

[AlonZivony]

When initializing the KernelSymbolTable via the NewKernelSymbolsMap, we give symbols without an owner the default owner value of "system".
This is problematic, because a module can call its owner "system", which will cause its symbols to look like they belong to the kernel.
The parsing of the owner also removes the '[' and ']' characters, which might cause corruption in the names parsed.
We should give some uninitialized value as the owner which could not be mocked by anyone so we can distinguish between system and module symbols.