Catch EPROTONOSUPPORT as a sign of no IPv6 as well (#41)

If IPv6 is disabled inside a freebsd jail, it seems this returns
EPROTONOSUPPORT and not EAFNOSUPPORT. In both cases, we should simply
try some other listed DNS servers.

Fixes [Bug #19928] https://bugs.ruby-lang.org/issues/19928

lib/resolv.rb

@@ -750,7 +750,7 @@ def lazy_initialize
               next if @socks_hash[bind_host]
               begin
                 sock = UDPSocket.new(af)
-              rescue Errno::EAFNOSUPPORT
+              rescue Errno::EAFNOSUPPORT, Errno::EPROTONOSUPPORT
                 next # The kernel doesn't support the address family.
               end
               @socks << sock