iproute2: suppress rtnl errors by default

Hi,

I already sent similar email about such questions but I will try again,
may be it was lost.

So when the up to date version of iproute2 is used on the older kernel
it might print the rtnl errors which is mostly related to case when old
kernel does not support some rtnl flags/types/attrs, so would not it be
better to suppress such messages by default but add a special command
line option which will enable them ?

Thanks,
Vadim Kochan