build: fix compile issue with missing/needed <endian.h> includes

Without adding in the include of <endian.h> in 2 files that
use functions/defines from it, we end up getting compiler errors
and linking errors.

Origin: #25

Author: Scott Kilau

common/crypto/ieee80211.c

@@ -17,6 +17,7 @@
  */
 #include <string.h>
 #include <stdint.h>
+#include <endian.h>
 #include <mbedtls/md.h>
 #include "common/specs/ieee80211.h"
 #include "common/specs/eapol.h"

common/ieee802154_frame.c

@@ -12,6 +12,7 @@
  * [1]: https://www.silabs.com/about-us/legal/master-software-license-agreement
  */
 #include <errno.h>
+#include <endian.h>
 
 #include "common/bits.h"
 #include "common/endian.h"