sd-device-monitor: fix ordering of setting buffer size

By b1c097af (#10239), the receive buffer
size for uevents was set by SO_RCVBUF at first, and fallback to
use SO_RCVBUFFORCE. So, as SO_RCVBUF limits to the buffer size
net.core.rmem_max, which is usually much smaller than 128MB udevd requests,
uevents buffer size was not sufficient.

This fixes the ordering of the request: SO_RCVBUFFORCE first, and
fallback to SO_RCVBUF. Then, udevd's uevent buffer size can be set to
128MB.

This also revert 90389323.

Fixes #11314 and #10754.

(cherry picked from commit ee0b9e72)