tree-wide: add a single version of "static const int one = 1"

All over the place we define local variables for the various sockopts
that take a bool-like "int" value. Sometimes they are const, sometimes
static, sometimes both, sometimes neither.

Let's clean this up, introduce a common const variable "const_int_one"
(as well as one matching "const_int_zero") and use it everywhere, all
acorss the codebase.

src/shared/ask-password-api.c

@@ -455,7 +455,6 @@ static int create_socket(char **ret) {
         _cleanup_free_ char *path = NULL;
         union sockaddr_union sa = {};
         _cleanup_close_ int fd = -1;
-        static const int one = 1;
         int salen;
 
         assert(ret);
@@ -476,7 +475,7 @@ static int create_socket(char **ret) {
                         return -errno;
         }
 
-        if (setsockopt(fd, SOL_SOCKET, SO_PASSCRED, &one, sizeof(one)) < 0)
+        if (setsockopt(fd, SOL_SOCKET, SO_PASSCRED, &const_int_one, sizeof(const_int_one)) < 0)
                 return -errno;
 
         *ret = TAKE_PTR(path);