Fix misalignment issues in TLVEncoder macros ENCODE_U16, ENCODE_U24

This commit resolves undefined behaviour runtime errors related
to misaligned memory access. E.g.

> openair3/NAS/COMMON/IES/FGSMobileIdentity.c:193:3:
> runtime error: store to misaligned address 0x608000021e2b for type 'uint16_t',
> which requires 2 byte alignment 0x608000021e2b: note: pointer points here 00 f1 ...

* ENCODE_U24: safely encode 24-bit values into a buffer
  by using memcpy to copy 3 bytes in network byte order (big-endian).
* ENCODE_U16: safely encodes a 16-bit value into a buffer, handling
  misalignment by memcpy 2 bytes to buffer in network byte order (big-endian).

openair3/NAS/COMMON/UTIL/TLVEncoder.h

@@ -28,13 +28,25 @@
     *(uint8_t*)(buffer) = value;    \
     size += sizeof(uint8_t)
 
-#define ENCODE_U16(buffer, value, size)   \
+/* Safely encodes a 16-bit value into a buffer, handling
-    *(uint16_t*)(buffer) = htons(value);  \
+   misalignment by memcpy 2 bytes to buffer in network
-   size += sizeof(uint16_t)
+   byte order (big-endian). */
+#define ENCODE_U16(buffer, value, size)        \
+  do {                                         \
+    uint16_t _val = htons(value);              \
+    memcpy((buffer), &_val, sizeof(uint16_t)); \
+    size += sizeof(uint16_t);                  \
+  } while (0)
 
-#define ENCODE_U24(buffer, value, size)   \
+/* Safely encodes a 24-bit value into a buffer, handling
-    *(uint32_t*)(buffer) = htonl(value);  \
+   misalignment by using htonl and memcpy to copy 3 bytes
-    size += sizeof(uint8_t) + sizeof(uint16_t)
+   in network byte order (big-endian). */
+#define ENCODE_U24(buffer, value, size)         \
+  do {                                          \
+    uint32_t _val = htonl(value);               \
+    memcpy((buffer), ((uint8_t*)&_val) + 1, 3); \
+    size += sizeof(uint8_t) + sizeof(uint16_t); \
+  } while (0)
 
 #define ENCODE_U32(buffer, value, size) \
   {                                     \