Iptables protocol by name not working

I have a problem using iptables with protocol name on LEDE 17.01.0.
iptables -A OUTPUT -o eth0 -d 224.0.0.0/8 -p vrrp -j ACCEPT
iptables v1.4.21: unknown protocol "vrrp" specified

using the protocol option with number is working (-p 112)

any idea?
thanks

Upstream iptables only recognizes protocols tcp, udp, udplite, icmp, esp, ah, sctp.

shouldn't /etc/protocols be read?
man page says "A protocol name from /etc/protocols is also allowed."
when I look in the source file xtables.c there is a line with getprotobyname
it has also worked in previous versions (OpenWrt)