Fix network specification via QEMU command line

[mkroening]

https://github.com/hermitcore/libhermit-rs/commit/eb2a46fe4d2892957a7e31fd8ce60bcd21a78f52 broke https://github.com/hermitcore/libhermit-rs/pull/337.

CC: @stlankes

[stlankes]

Help me, what doesn't work?

[mkroening]

https://github.com/hermitcore/libhermit-rs/pull/337 parses QEMU args and puts the values into environment variables of the application. This was received before via std::env::var in hermit-sys. Now the env vars are required at compile time, so the values from QEMU's command line don't end up anywhere.

This is not a problem that I have experienced but this currently breaks runh, if I am not mistaken. We could either:

• Make runh recompile the kernel each time with the corresponding values. or
• Let libhermit-rs::env not put the parsed values into the app's environment but deliver them to libhermit-rs::net directly.