fix get_addr() and get_prefix() error messages

fix get_addr() and get_prefix() error messages

An attempt to add invalid address to interface would print "???" string
instead of the address family name.

For example:
$ ip address add 256.10.166.1/24 dev ens8
Error: ??? prefix is expected rather than "256.10.166.1/24".

$ ip neighbor add proxy 2001:db8::g dev ens8
Error: ??? address is expected rather than "2001:db8::g".

With this patch the output will look like:
$ ip address add 256.10.166.1/24 dev ens8
Error: inet prefix is expected rather than "256.10.166.1/24".

$ ip neighbor add proxy 2001:db8::g dev ens8
Error: inet6 address is expected rather than "2001:db8::g".

Signed-off-by: Przemyslaw Szczerbik <przemyslawx.szczerbik@intel.com>
Signed-off-by: Marco Varlese <marco.varlese@intel.com>