Change some openbsd errors to warnings to allow system monitor to run.

Changes

• Change netload kvm_nlist and kvm_read error to warnings
• Change ppp kvm_nlist error to warning
• Change suid_open kvm_openfiles error text from kvm_open to kvm_openfiles

These changes allow the gnome-system-monitor to run when compiled with -Dsystemd=false on openbsd.
Running the system monitor built like that causes continuous log spam and the network io measurements don't work.
Everything else however seems to be fully functional.