NM_UTILS_ERROR is our way to say, that we don't care about
the GError domain and code. nmcli sometimes passes domain "1"
and code "0" to g_set_error(), which could be considered
a bug.
We usually don't care about the error but only about the error
message, so let's have a universally available error quark around.
_nm_utils_ascii_str_to_int64() was declared in libnm-core's internal
header "nm-core-internal.h" and thus available for libnm-core, libnm,
NetworkManager and related.
It also means, the function was not available in libnm-util, libnm-glib,
clients or dispatcher. So, we either reimplemented it (nmc_string_to_int_base)
or struggle with the awkward strtol* API.
