Add buffer_read16be()

Add a function to read 16 bits in big-endian to a uint16_t.

app/src/buffer_util.h

@@ -18,6 +18,11 @@ buffer_write32be(uint8_t *buf, uint32_t value) {
     buf[3] = value;
 }
 
+static inline uint16_t
+buffer_read16be(const uint8_t *buf) {
+    return (buf[0] << 8) | buf[1];
+}
+
 static inline uint32_t
 buffer_read32be(const uint8_t *buf) {
     return (buf[0] << 24) | (buf[1] << 16) | (buf[2] << 8) | buf[3];