deps: bump rtnetlink 0.20.0 to 0.21.0

Pulls netlink-packet-route 0.30.0, which adds DEVCONF_FORCE_FORWARDING
to Inet6DevConf for kernel 6.17+. Closes the IFLA_INET6_CONF WARN
observed on kernel-6.17 hosts during fips startup.

Zero source edits: FIPS does not use the deprecated
link_local_address API or the renamed StablePrivacy display path.

Live-host WARN-absence verification on a kernel-6.17 host is
scheduled for a separate deploy.

Cargo.lock

@@ -1809,9 +1809,9 @@ dependencies = [
 
 [[package]]
 name = "netlink-packet-route"
-version = "0.28.0"
+version = "0.30.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "4ce3636fa715e988114552619582b530481fd5ef176a1e5c1bf024077c2c9445"
+checksum = "be8919612f6028ab4eacbbfe1234a9a43e3722c6e0915e7ff519066991905092"
 dependencies = [
  "bitflags 2.11.1",
  "libc",
@@ -2632,9 +2632,9 @@ dependencies = [
 
 [[package]]
 name = "rtnetlink"
-version = "0.20.0"
+version = "0.21.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "4b960d5d873a75b5be9761b1e73b146f52dddcd27bac75263f40fba686d4d7b5"
+checksum = "dc19f84f710fa2f337617f9bc0400260a94224bde7bae28fd8879f3771ca5784"
 dependencies = [
  "futures-channel",
  "futures-util",