file: /proc/sys/net/ipv4/conf/interface/arp_notify
variable: net.ipv4.conf.interface.arp_notify
Official reference

Define mode for notification of address and device changes. 0 - (default): do nothing 1 - Generate gratuitous arp requests when device is brought up or hardware address changes.

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