net: RTNETLINK adjusting values of min_ifinfo_dump_size

Setting link parameters on a netdevice changes the value
of if_nlmsg_size(), therefore it is necessary to recalculate
min_ifinfo_dump_size.

Signed-off-by: Stefan Gula <steweg@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>