slstatus.h: Fix coding style

Function declarations should include variable names.
For functions with different parameters on different platfroms they are
left out.

slstatus.h

@@ -3,20 +3,20 @@
 /* battery */
 const char *battery_perc(const char *);
 const char *battery_state(const char *);
-const char *battery_remaining(const char*);
+const char *battery_remaining(const char *);
 
 /* cpu */
 const char *cpu_freq(void);
 const char *cpu_perc(void);
 
 /* datetime */
-const char *datetime(const char *);
+const char *datetime(const char *fmt);
 
 /* disk */
-const char *disk_free(const char *);
-const char *disk_perc(const char *);
-const char *disk_total(const char *);
-const char *disk_used(const char *);
+const char *disk_free(const char *mnt);
+const char *disk_perc(const char *mnt);
+const char *disk_total(const char *mnt);
+const char *disk_used(const char *mnt);
 
 /* entropy */
 const char *entropy(void);
@@ -25,8 +25,8 @@ const char *entropy(void);
 const char *hostname(void);
 
 /* ip */
-const char *ipv4(const char *);
-const char *ipv6(const char *);
+const char *ipv4(const char *iface);
+const char *ipv6(const char *iface);
 
 /* kernel_release */
 const char *kernel_release(void);
@@ -38,14 +38,14 @@ const char *keyboard_indicators(void);
 const char *keymap(void);
 
 /* load_avg */
-const char *load_avg(const char *);
+const char *load_avg(void);
 
 /* netspeeds */
-const char *netspeed_rx(const char *);
-const char *netspeed_tx(const char *);
+const char *netspeed_rx(const char *interface);
+const char *netspeed_tx(const char *interface);
 
 /* num_files */
-const char *num_files(const char *);
+const char *num_files(const char *dir);
 
 /* ram */
 const char *ram_free(void);
@@ -54,7 +54,7 @@ const char *ram_total(void);
 const char *ram_used(void);
 
 /* run_command */
-const char *run_command(const char *);
+const char *run_command(const char *cmd);
 
 /* swap */
 const char *swap_free(void);
@@ -74,8 +74,8 @@ const char *username(void);
 const char *uid(void);
 
 /* volume */
-const char *vol_perc(const char *);
+const char *vol_perc(const char *card);
 
 /* wifi */
-const char *wifi_perc(const char *);
-const char *wifi_essid(const char *);
+const char *wifi_perc(const char *iface);
+const char *wifi_essid(const char *iface);