net/AddressInfo: add MakeAddrInfo()

src/net/AddressInfo.hxx

@@ -40,6 +40,17 @@
 #include <netdb.h>
 #endif
 
+constexpr struct addrinfo
+MakeAddrInfo(int flags, int family, int socktype, int protocol=0) noexcept
+{
+	struct addrinfo ai{};
+	ai.ai_flags = flags;
+	ai.ai_family = family;
+	ai.ai_socktype = socktype;
+	ai.ai_protocol = protocol;
+	return ai;
+}
+
 class AddressInfo : addrinfo {
 	/* this class cannot be instantiated, it can only be cast from
 	   a struct addrinfo pointer */

src/net/Resolver.cxx

@@ -149,10 +149,6 @@ Resolve(const char *host_and_port, int default_port,
 AddressInfoList
 Resolve(const char *host_port, unsigned default_port, int flags, int socktype)
 {
-	struct addrinfo hints{};
-	hints.ai_flags = flags;
-	hints.ai_family = AF_UNSPEC;
-	hints.ai_socktype = socktype;
-
+	const auto hints = MakeAddrInfo(flags, AF_UNSPEC, socktype);
 	return Resolve(host_port, default_port, &hints);
 }