Validate IPv6 modes in API when IP version is 4

Add a validation to ipv6_ra_mode and ipv6_address_mode with ip
version. An InvalidInput error is prompted when ipv6_ra_mode
or ipv6_address_mode is specified in subnet create and update
API and ip version is 4.

Change-Id: I9a0356f23e6b162c31f2d289a34f4bd261cee91e
Closes-Bug: 1307788
Merge "Validate IPv6 modes in API when IP version is 4"