fixup! posix_sockets: make pool type its own type

This reverts commit 5ee26bb.

Not required anymore due to sock_async callback arguments

sys/posix/sockets/posix_sockets.c

@@ -99,12 +99,8 @@ typedef struct {
     sock_tcp_ep_t local;        /* to store bind before connect/listen */
 } socket_t;
 
-typedef struct {
-    socket_sock_t sock;
-} socket_sock_pool_t;
-
 static socket_t _socket_pool[_ACTUAL_SOCKET_POOL_SIZE];
-static socket_sock_pool_t _sock_pool[SOCKET_POOL_SIZE];
+static socket_sock_t _sock_pool[SOCKET_POOL_SIZE];
 #ifdef MODULE_SOCK_TCP
 static sock_tcp_t _tcp_sock_pool[SOCKET_POOL_SIZE][SOCKET_TCP_QUEUE_SIZE];
 #endif
@@ -144,7 +140,7 @@ static socket_sock_t *_get_free_sock(void)
     if (i < 0) {
         return NULL;
     }
-    return &_sock_pool[i].sock;
+    return &_sock_pool[i];
 }
 
 static socket_t *_get_socket(int fd)
@@ -166,11 +162,10 @@ static socket_t *_get_socket(int fd)
 
 static int _get_sock_idx(socket_sock_t *sock)
 {
-    if ((sock < &_sock_pool[0].sock) ||
-        (sock > &_sock_pool[SOCKET_POOL_SIZE - 1].sock)) {
+    if ((sock < &_sock_pool[0]) || (sock > &_sock_pool[SOCKET_POOL_SIZE - 1])) {
         return -1;
     }
-    return sock - &_sock_pool[0].sock;
+    return sock - &_sock_pool[0];
 }
 
 static inline int _choose_ipproto(int type, int protocol)