tools/syz-symbolize: use -config to support module symbolize

[jiangenj]

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[a-nogikh]

Hi Joey!

I'd suggest that we add -config as an optional parameter for syz-symbolize instead of only accepting the syz-manager-config. I.e. if flagConfig is specified, use it, otherwise rely on the remaining parameters.

The full syz-manager config, which is required by mgrconfig.LoadFile, is much larger and more rigorously checked than the small piece of it generated here for mgrconfig.LoadPartialData.

[jiangenj]

@a-nogikh updated, please review again.