MINOR: protocol: add the control layer type in the protocol struct

This one will be needed to more accurately select a protocol. It may
differ from the socket type for QUIC, which uses dgram at the socket
layer and provides stream at the control layer. The upper level requests
a control layer only so we need this field.
diff --git a/src/proto_udp.c b/src/proto_udp.c
index d408d7c..74408b4 100644
--- a/src/proto_udp.c
+++ b/src/proto_udp.c
@@ -48,6 +48,7 @@
 static struct protocol proto_udp4 = {
 	.name = "udp4",
 	.fam = &proto_fam_inet4,
+	.ctrl_type = SOCK_DGRAM,
 	.sock_domain = AF_CUST_UDP4,
 	.sock_type = SOCK_DGRAM,
 	.sock_prot = IPPROTO_UDP,
@@ -67,6 +68,7 @@
 static struct protocol proto_udp6 = {
 	.name = "udp6",
 	.fam = &proto_fam_inet6,
+	.ctrl_type = SOCK_DGRAM,
 	.sock_domain = AF_CUST_UDP6,
 	.sock_type = SOCK_DGRAM,
 	.sock_prot = IPPROTO_UDP,