fix(nvmf): nvme list-subsys prints the address using commas as separator

fix(nvmf): nvme list-subsys prints the address using commas as separator

nvme-cli 1.x printed the address using spaces as separator, but nvme-cli 2.x
prints the address using commas as separator (exact output from sysfs). E.g.,
output from `cat /sys/class/nvme/nvme0/address`:

traddr=nn-0x201700a09890f5bf:pn-0x201900a09890f5bf,host_traddr=nn-0x200000109b579ef5:pn-0x100000109b579ef5

Also, I suppress rd.nvmf.discover= cmdline option if all fields are empty.