Resolve TODO: Use IFLA_LINKINFO to detect tun/tap/wireguard/ppp interfaces

[ayushrawat-10]

This PR replaces the previous sysfs-based interface type detection with a netlink-based implementation using IFLA_LINKINFO.
This resolves the existing inline TODO in netlink.rs:
// TODO: use netlink for these too
Interface types such as tun, tap, wireguard, and ppp are now detected directly from netlink attributes instead of relying on /sys/class/net.

Things Changed

1. Removed sysfs-based detection

The following logic was removed:

• Probing /sys/class/net//tun_flags
• Parsing /sys/class/net//uevent
• String-based detection of wireguard and ppp
  This eliminates filesystem access and string scanning for interface classification.

2. Added netlink-based link type detection

We now extract interface type from the IFLA_LINKINFO attribute:
Ifla::Linkinfo => link_type = extract_link_type(attr.payload().as_ref()),
And a fucntion
fn extract_link_type(linkinfo_bytes: &[u8]) -> Option<String>

Why This Change?

1. More Correct

• Netlink is the authoritative source of network interface metadata.
• Relying on sysfs and filename heuristics is less robust and more indirect.

2. More Efficient

• Removes filesystem lookups
• Avoids async file reads
• Avoids string scanning of uevent.
  Everything is now derived directly from netlink data already being processed.

Impact
No functional changes are expected.
Interface classification now relies solely on netlink metadata instead of sysfs probing.