Panic when MulticastInterfaces/Regex has errors.

[shibe2]

Current behavior

https://github.com/yggdrasil-network/yggdrasil-go/blob/49c424ef213589d63215f10dc1958b2e93fb1e6c/cmd/yggdrasil/main.go#L242

MustCompile is like Compile but panics if the expression cannot be parsed.

Expected behavior

Print a message that points to MulticastInterfaces and includes error from regexp.Compile. Then either exit or ignore the erroneous entry.

[Slex]

This looks like expected behavior: almost all config errors cause panic

[shibe2]

almost all config errors cause panic

Gross.