net/beanstalkd: fix build on 32-bits by specifying correct format specifier

net.c:162:21: error: format specifies type 'long' but the argument has type 'unsigned int' [-Werror,-Wformat]

path, strlen(path), maxlen);
      ^~~~~~~~~~~~

net.c:162:35: error: format specifies type 'long' but the argument has type 'size_t' (aka 'unsigned int') [-Werror,-Wformat]

path, strlen(path), maxlen);
                    ^~~~~~