fix get_local_ipaddr for IPv6-only #158

Job	Run time
Rustfmt	13s
Check (ubuntu-latest)	20s
Check (windows-latest)	39s
Cross compile (i686-unknown-linux-musl)	42s
Cross compile (x86_64-unknown-freebsd)	40s
Cross compile (armv7-linux-androideabi)	52s
Cross compile (x86_64-unknown-netbsd)	36s
Cross compile (aarch64-linux-android)	54s
Cross compile (x86_64-unknown-linux-musl)	44s
Check (macOS-latest)	17s
	5m 57s

Provide feedback