socketlib: Fallback to IPv4 when IPv6 not present.
socketlib: Fallback to IPv4 when IPv6 not present.

This fixes systems where IPv6 is available in libraries but just not enabled
in the kernel.

narakai/shairport,bowlofstew/shairport,skaman/shairport,bowlofstew/shairport,dotmpe/shairport,IronBeard/shairport,mspasov/shairport,hendrikw82/shairport,mspasov/shairport,IronBeard/shairport,dotmpe/shairport,albertz/shairport,narakai/shairport,hendrikw82/shairport,bowlofstew/shairport,IronBeard/shairport,skaman/shairport,narakai/shairport,albertz/shairport,hendrikw82/shairport,dotmpe/shairport