Fix DIAL processing by updating Host header & correcting off-by-one errors

[ryman1]

• I added additional DIAL proxy functionality that updates the Host HTTP request header to match the target DIAL server's address. Without this functionality, some DIAL servers (e.g. TV with ROKU integrated) refuse to respond when the Host header is not as expected. Once updated, the Host request header contains the proxy server's interface address found on the DIAL client's network segment.
• Off by one errors were corrupting packets when handling the buffers used for resizing and updating DIAL packets, causing DIAL processing to fail.
• When DIAL operations replaced packet contents with the proxy's IP, the length change of the packets, when the IP address string character counts varied, was not being considered, leading to data outside the buffer being sent over the socket. The len = len + lengthChange; entries correct this.

Tested successfully with udpbroadcastrelay running on Ubuntu 20.04.6, relaying Youtube SmartTV DIAL, chromecast, airplay, and MDNS

[diizzyy]

Hi,

This fails to compile,

--- all ---
cc -O2 -pipe -march=tigerlake  -fstack-protector-strong -fno-strict-aliasing -std=c99  -g main.c -o udpbroadcastrelay
main.c:1210:14: error: use of undeclared identifier 'proxyDialHttpHostHeader'
 1210 |     else if (proxyDialHttpHostHeader && socktype == LOCSVC_CIENTSOCK)
      |              ^
1 error generated.