socket/sockopt: kernel timestamping support

[utkarshgupta137]

I'm trying to switch away from nix/libc to this crate & I found that rustix currently doesn't provide functions for using kernel timestamping. The nix crate provides the following required for kernel timestamping:

• sockopt: ReceiveTimestamp
• sockopt: ReceiveTimestampns
• sockopt: Timestamping
• sockopt: TimestampingFlag (for Timestamping)
• socket: ControlMessageOwned::ScmTimestamp (for ReceiveTimestamp)
• socket: ControlMessageOwned::ScmTimestampns (for ReceiveTimestampns)
• socket: ControlMessageOwned::ScmTimestampsns (for Timestamping)
• socket: Timestamps (for Timestamping)

I'm willing to work on a PR contributing a similar API (with individual functions for each sockopt variant, as is the rustix way).