r0 = socket$inet6_udp(0xa, 0x2, 0x0)
setsockopt$inet6_mtu(r0, 0x29, 0x17, &(0x7f00000000c0)=0x5, 0x4)
sendmmsg$inet6(r0, &(0x7f0000002280)=[{{&(0x7f0000000040)={0xa, 0x4e21, 0x0, @mcast1}, 0x1c, 0x0}}], 0x1, 0x0)