udev: open control and netlink sockets before daemonization

c4b69e99 effectively moved the initalization of socket.
Before that commit:
run → listen_fds → udev_ctrl_new → udev_ctrl_new_from_fd → socket()
After:
run → main_loop → manager_new → udev_ctrl_new_from_fd → socket()

The problem is that main_loop was called after daemonization. Move manager_new
out of main_loop and before daemonization.

Fixes #11314 (hopefully ;)).

v2: Yu Watanabe
sd_event is initialized in main_loop().