pid1: do not fail if we get EPERM while setting up network name

pid1: do not fail if we get EPERM while setting up network name

In a user namespace container:
Feb 28 12:45:53 0b2420135953 systemd[1]: Starting Home Manager...
Feb 28 12:45:53 0b2420135953 systemd[21]: systemd-homed.service: Failed to set up network namespacing: Operation not permitted
Feb 28 12:45:53 0b2420135953 systemd[21]: systemd-homed.service: Failed at step NETWORK spawning /usr/lib/systemd/systemd-homed: Operation not permitted
Feb 28 12:45:53 0b2420135953 systemd[1]: systemd-homed.service: Main process exited, code=exited, status=225/NETWORK
Feb 28 12:45:53 0b2420135953 systemd[1]: systemd-homed.service: Failed with result 'exit-code'.
Feb 28 12:45:53 0b2420135953 systemd[1]: Failed to start Home Manager.

We should treat this similarly to the case where network namespace are not
supported at all.

https://bugzilla.redhat.com/show_bug.cgi?id=1807465