net: sockets: Specify alignment for sockaddr* structs

To avoid misalignment errors when casting between
sockaddr_storage/sockaddr and specialied sockaddr_* variants, specify
alignment for the former to match the alignment of the others.

The issue was reported by UBSAN:

  utils.c:802:8: runtime error: member access within misaligned
  address 0xf4aff186 for type 'struct sockaddr_in6', which requires
  4 byte alignment

Signed-off-by: Robert Lubos <robert.lubos@nordicsemi.no>

Author: rlubos

include/zephyr/net/net_ip.h

@@ -404,26 +404,28 @@ struct cmsghdr {
 
 /** @endcond */
 
+#define SOCKADDR_ALIGN (4)
+
 /** Generic sockaddr struct. Must be cast to proper type. */
 struct sockaddr {
 	sa_family_t sa_family; /**< Address family */
 /** @cond INTERNAL_HIDDEN */
 	char data[NET_SOCKADDR_MAX_SIZE - sizeof(sa_family_t)];
 /** @endcond */
-};
+} __aligned(SOCKADDR_ALIGN);
 
 /** @cond INTERNAL_HIDDEN */
 
 struct sockaddr_ptr {
 	sa_family_t family;
 	char data[NET_SOCKADDR_PTR_MAX_SIZE - sizeof(sa_family_t)];
-};
+} __aligned(SOCKADDR_ALIGN);
 
 /* Same as sockaddr in our case */
 struct sockaddr_storage {
 	sa_family_t ss_family;
 	char data[NET_SOCKADDR_MAX_SIZE - sizeof(sa_family_t)];
-};
+} __aligned(SOCKADDR_ALIGN);
 
 /* Socket address struct for UNIX domain sockets */
 struct sockaddr_un {