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

Minimum hop limit Information in Router Advertisement.

Hop limit Information in Router Advertisement less than this variable shall be ignored.

Default: 1

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