file: /proc/sys/net/ipv6/conf/interface/accept_ra
variable: net.ipv6.conf.interface.accept_ra
Official reference

Accept Router Advertisements; autoconfigure using them.

It also determines whether or not to transmit Router Solicitations. If and only if the functional setting is to accept Router Advertisements, Router Solicitations will be transmitted.

Possible values are: 0 Do not accept Router Advertisements. 1 Accept Router Advertisements if forwarding is disabled. 2 Overrule forwarding behaviour. Accept Router Advertisements even if forwarding is enabled.

Functional default: enabled if local forwarding is disabled. disabled if local forwarding is enabled.

Nb: per interface setting (where “interface” is the name of your network interface); “all” is a special interface: changes the settings for all interfaces.