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

If set, allows processes to bind() to non-local IPv6 addresses, which can be quite useful - but may break some applications. Default: 0

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