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_tcp.c b/src/proto_tcp.c
index 33d39b3..09d3e86 100644
--- a/src/proto_tcp.c
+++ b/src/proto_tcp.c
@@ -52,6 +52,7 @@
 static struct protocol proto_tcpv4 = {
 	.name = "tcpv4",
 	.fam = &proto_fam_inet4,
+	.ctrl_type = SOCK_STREAM,
 	.sock_domain = AF_INET,
 	.sock_type = SOCK_STREAM,
 	.sock_prot = IPPROTO_TCP,
@@ -71,6 +72,7 @@
 static struct protocol proto_tcpv6 = {
 	.name = "tcpv6",
 	.fam = &proto_fam_inet6,
+	.ctrl_type = SOCK_STREAM,
 	.sock_domain = AF_INET6,
 	.sock_type = SOCK_STREAM,
 	.sock_prot = IPPROTO_TCP,