Fix buffer end location (#447)

Fix payload buffer to end at actual payload end. UDP header length includes the 8 bytes of the header so we do not want the +8 at the end of the buffer.

Signed-off-by: noiz <noiz@users.noreply.github.com>

Co-authored-by: Pablo Mazzini <pmazzini@gmail.com>

dhcpv4/client4/client.go

@@ -322,7 +322,7 @@ func (c *Client) SendReceive(sendFd, recvFd int, packet *dhcpv4.DHCPv4, messageT
 			}
 			// UDP checksum is not checked
 			pLen := int(binary.BigEndian.Uint16(udph[4:6]))
-			payload := buf[iph.Len+8 : iph.Len+8+pLen]
+			payload := buf[iph.Len+8 : iph.Len+pLen]
 
 			response, innerErr = dhcpv4.FromBytes(payload)
 			if innerErr != nil {