extconf.rb: fix warnings

* ext/socket/extconf.rb: fix warnings from IN6_IS_ADDR_ macros in
  apple's netinet6/in6.rb.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@38946 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
* remove trailing spaces.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@38947 b2dd03c8-39d4-4d8f-98ff-823fe69b080e