socket.c: suppress warnings

* ext/socket/socket.c (rsock_sys_fail_sockaddr): cast down explicitly
  to suppress warnings.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@40155 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
socket/extconf.rb: RSTRING_SOCKLEN

* ext/socket/extconf.rb (RSTRING_SOCKLEN): macro to cast RSTRING_LEN
  to socklen_t.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@40156 b2dd03c8-39d4-4d8f-98ff-823fe69b080e