MII: fix Kconfig dependencies for MII

MII Kconfig option is apart of the core networking drivers and
by default NET_CORE is enabled so drivers selecting MII will
have MII enabled as well.  It was found using the randconfig
option during testing, MII would be selected but NET_CORE
could be disabled.  This caused a dependency error.

Resolved the dependency by selecting NET_CORE when MII is
selected.

Reported-by: Emil Tantilov <emil.s.tantilov@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/ethernet/realtek/Kconfig b/drivers/net/ethernet/realtek/Kconfig
index d8df67a..84083ec 100644
--- a/drivers/net/ethernet/realtek/Kconfig
+++ b/drivers/net/ethernet/realtek/Kconfig
@@ -37,6 +37,7 @@
 	tristate "RealTek RTL-8139 C+ PCI Fast Ethernet Adapter support (EXPERIMENTAL)"
 	depends on PCI && EXPERIMENTAL
 	select CRC32
+	select NET_CORE
 	select MII
 	---help---
 	  This is a driver for the Fast Ethernet PCI network cards based on
@@ -51,6 +52,7 @@
 	tristate "RealTek RTL-8129/8130/8139 PCI Fast Ethernet Adapter support"
 	depends on PCI
 	select CRC32
+	select NET_CORE
 	select MII
 	---help---
 	  This is a driver for the Fast Ethernet PCI network cards based on
@@ -105,6 +107,7 @@
 	depends on PCI
 	select FW_LOADER
 	select CRC32
+	select NET_CORE
 	select MII
 	---help---
 	  Say Y here if you have a Realtek 8169 PCI Gigabit Ethernet adapter.