Fix typo endianess -> endianness

Rename contrib/struct_endianess.py to contrib/struct_endianness.py, and
fix the typo everywhere. This is in preparation to call the script in
CI on all repositories.

Related: OS#5884
Change-Id: Idc4af9098ba1de26243464c772d6ea8be330646a
diff --git a/include/osmocom/gsm/protocol/gsm_44_004.h b/include/osmocom/gsm/protocol/gsm_44_004.h
index 616e436..c30ba0c 100644
--- a/include/osmocom/gsm/protocol/gsm_44_004.h
+++ b/include/osmocom/gsm/protocol/gsm_44_004.h
@@ -12,7 +12,7 @@
 			reserved:1;
 		uint8_t ta;
 #elif OSMO_IS_BIG_ENDIAN
-/* auto-generated from the little endian part above (libosmocore/contrib/struct_endianess.py) */
+/* auto-generated from the little endian part above (libosmocore/contrib/struct_endianness.py) */
 		uint8_t	reserved:1, srr_sro:1, fpc_epc:1, ms_pwr:5;
 		uint8_t ta;
 #endif