net: add tcp_default_read_timeout and tcp_default_write_timeout and use them consistently

examples/net_raw_http.v

@@ -1,15 +1,14 @@
-// Simple raw HTTP head request
 import net
 import io
 
-// Make a new connection
-mut conn := net.dial_tcp('google.com:80')?
-defer { conn.close() }
-// Simple http HEAD request for a file
-conn.write_str('HEAD /index.html HTTP/1.0\r\n\r\n')?
-// Make sure to set a timeout so we can wait for a response!
-conn.set_read_timeout(net.infinite_timeout)
-// Read all the data that is waiting
-result := io.read_all(conn)?
-// Cast to string and print result
-println(result.bytestr())
+fn main() {
+	// Make a new connection
+	mut conn := net.dial_tcp('google.com:80')?
+	defer { conn.close() }
+	// Simple http HEAD request for a file
+	conn.write_str('HEAD /index.html HTTP/1.0\r\n\r\n')?
+	// Read all the data that is waiting
+	result := io.read_all(conn)?
+	// Cast to string and print result
+	println(result.bytestr())
+}