tsi_hijack_unix should be added to the guest kernel cmdline if on Linux

[karuboniru]

Since containers/libkrunfw@52926f8, tsi_hijack_unix won't be enabled by default, adding extra flag tsi_hijack_unix would be required to enable this. At least for containers, this will enable more fluent transition from crun to krun.

[mtjhrc]

I added a proper API for configuring this in #483

Question remains what should be the default, enabled or disabled.... Having it enabled might potentially break some stuff within the guest, on the other hand having this enabled is pretty cool too...

@slp

[karuboniru]

That would be nice, the change would be just a function call from krun.

BTW, when I am testing, I found that the tsi for unix socket only works when the vm tries to connect socket created by host but not vice versa, is this by design or I am making mistake? nevermind this, it is related to SELinux on my side