scheduling: Move friends' definitions outside the class scope
scheduling: Move friends' definitions outside the class scope

Friend function definitions inside the class are not allowed to have a
namespace specifier attached. Moving friend functions bodies from
scheduling_group to the internal:: namespace.

This fix enables Seastar compilation with Clang.

Signed-off-by: Vladimir Krivopalov <8393b6f566d8ebdefd4d2517fe16f44423413d9c@gmail.com>
Message-Id: <20180617235924.1036-1-8393b6f566d8ebdefd4d2517fe16f44423413d9c@gmail.com>

cloudius-systems/seastar,avikivity/seastar,scylladb/seastar,cloudius-systems/seastar,syuu1228/seastar,syuu1228/seastar,dreamsxin/seastar,syuu1228/seastar,scylladb/seastar,avikivity/seastar,avikivity/seastar,cloudius-systems/seastar,dreamsxin/seastar,dreamsxin/seastar,scylladb/seastar