net: dsa: restrict SMSC_LAN9303_I2C kconfig

Since kconfig 'select' does not follow dependency chains, if symbol KSA
selects KSB, then KSA should also depend on the same symbols that KSB
depends on, in order to prevent Kconfig warnings and possible build
errors.

Change NET_DSA_SMSC_LAN9303_I2C and NET_DSA_SMSC_LAN9303_MDIO so that
they are limited to VLAN_8021Q if the latter is enabled. This prevents
the Kconfig warning:

WARNING: unmet direct dependencies detected for NET_DSA_SMSC_LAN9303
  Depends on [m]: NETDEVICES [=y] && NET_DSA [=y] && (VLAN_8021Q [=m] || VLAN_8021Q [=m]=n)
  Selected by [y]:
  - NET_DSA_SMSC_LAN9303_I2C [=y] && NETDEVICES [=y] && NET_DSA [=y] && I2C [=y]

Fixes: 430065e2

 ("net: dsa: lan9303: add VLAN IDs to master device")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Andrew Lunn <andrew@lunn.ch>
Cc: Vivien Didelot <vivien.didelot@gmail.com>
Cc: Florian Fainelli <f.fainelli@gmail.com>
Cc: Vladimir Oltean <olteanv@gmail.com>
Cc: Juergen Borleis <jbe@pengutronix.de>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Paolo Abeni <pabeni@redhat.com>
Cc: Mans Rullgard <mans@mansr.com>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>