Rename packet_len to data_len

This makes the distinction clearer between the length of the USB packet
and the length of the data its CCID header references

src/pipe.rs

@@ -152,7 +152,7 @@ where
             // TODO check
             self.ext_packet.extend_from_slice(&packet).unwrap();
 
-            let pl = packet.packet_len();
+            let pl = packet.data_len();
             if pl > PACKET_SIZE - CCID_HEADER_LEN {
                 self.receiving_long = true;
                 self.in_chain = 1;

src/types/packet.rs

@@ -6,11 +6,11 @@ pub type RawPacket = heapless::Vec<u8, PACKET_SIZE>;
 pub type ExtPacket = heapless::Vec<u8, MAX_MSG_LENGTH>;
 
 pub trait RawPacketExt {
-    fn packet_len(&self) -> usize;
+    fn data_len(&self) -> usize;
 }
 
 impl RawPacketExt for RawPacket {
-    fn packet_len(&self) -> usize {
+    fn data_len(&self) -> usize {
         u32::from_le_bytes(self[1..5].try_into().unwrap()) as usize
     }
 }