fix(dhcp): can not renew an ip address

The dhcp server is systemd-networkd, and the dhcp
plugin can request an ip but can not renew it.
The systemd-networkd just ignore the renew request.

```
2024/09/14 21:46:00 no DHCP packet received within 10s
2024/09/14 21:46:00 retrying in 31.529038 seconds
2024/09/14 21:46:42 no DHCP packet received within 10s
2024/09/14 21:46:42 retrying in 63.150490 seconds
2024/09/14 21:47:45 98184616c91f15419f5cacd012697f85afaa2daeb5d3233e28b0ec21589fb45a/iot/eth1: no more tries
2024/09/14 21:47:45 98184616c91f15419f5cacd012697f85afaa2daeb5d3233e28b0ec21589fb45a/iot/eth1: renewal time expired, rebinding
2024/09/14 21:47:45 Link "eth1" down. Attempting to set up
2024/09/14 21:47:45 98184616c91f15419f5cacd012697f85afaa2daeb5d3233e28b0ec21589fb45a/iot/eth1: lease rebound, expiration is 2024-09-14 22:47:45.309270751 +0800 CST m=+11730.048516519
```

Follow the https://datatracker.ietf.org/doc/html/rfc2131#section-4.3.6,
following options must not be sent in renew

- Requested IP Address
- Server Identifier

Since the upstream code has been inactive for 6 years,
we should switch to another dhcpv4 library.
The new selected one is https://github.com/insomniacslk/dhcp.

Signed-off-by: Songmin Li <lisongmin@protonmail.com>

vendor/github.com/insomniacslk/dhcp/dhcpv4/option_strings.go

@@ -0,0 +1,55 @@
+package dhcpv4
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/u-root/uio/uio"
+)
+
+// Strings represents an option encapsulating a list of strings in IPv4 DHCP as
+// specified in RFC 3004
+//
+// Strings implements the OptionValue type.
+type Strings []string
+
+// FromBytes parses Strings from a DHCP packet as specified by RFC 3004.
+func (o *Strings) FromBytes(data []byte) error {
+	buf := uio.NewBigEndianBuffer(data)
+	if buf.Len() == 0 {
+		return fmt.Errorf("Strings DHCP option must always list at least one String")
+	}
+
+	*o = make(Strings, 0)
+	for buf.Has(1) {
+		ucLen := buf.Read8()
+		if ucLen == 0 {
+			return fmt.Errorf("DHCP Strings must have length greater than 0")
+		}
+		*o = append(*o, string(buf.CopyN(int(ucLen))))
+	}
+	return buf.FinError()
+}
+
+// ToBytes marshals Strings to a DHCP packet as specified by RFC 3004.
+func (o Strings) ToBytes() []byte {
+	buf := uio.NewBigEndianBuffer(nil)
+	for _, uc := range o {
+		buf.Write8(uint8(len(uc)))
+		buf.WriteBytes([]byte(uc))
+	}
+	return buf.Data()
+}
+
+// String returns a human-readable representation of a list of Strings.
+func (o Strings) String() string {
+	return strings.Join(o, ", ")
+}
+
+// OptRFC3004UserClass returns a new user class option according to RFC 3004.
+func OptRFC3004UserClass(v []string) Option {
+	return Option{
+		Code:  OptionUserClassInformation,
+		Value: Strings(v),
+	}
+}