New TOS (per socket) options

[nikbyte]

Summary
This PR introduces two key changes:

1. Allows setting the global TOS (Type of Service) parameter to 0 to disable the IP_TOS socket option.
2. Adds a per-socket parameter tos, allowing TOS to be set on a per-socket basis. If this parameter is set, it overrides the global value.

Details
Previously, the global TOS parameter could not be set to 0, meaning that disabling the IP_TOS socket option was not straightforward. This PR introduces the ability to explicitly set TOS=0, ensuring that no IP_TOS is applied.

Additionally, this PR introduces a new per-socket tos parameter, which enables granular control over TOS settings on an individual socket level. If a socket-specific value is provided, it takes precedence over the global setting, allowing for more flexible traffic prioritization configurations.

Solution

• Modified the global TOS handling logic to allow 0 as a valid value.
• Introduced a per-socket tos parameter in the socket configuration.
• Ensured that when the per-socket tos value is set, it overrides the global TOS setting.
• Maintained backward compatibility by preserving previous behaviors unless explicitly overridden.

Compatibility

• This change maintains backward compatibility as existing configurations remain unchanged unless explicitly modified.
• The ability to set TOS=0 does not affect existing deployments but provides more flexibility.
• The per-socket tos parameter is an additional feature that does not interfere with existing configurations.