MDEV-22137 correct documentation of tcp_keepalive_time system variable

Author: vaintroub

mysql-test/main/mysqld--help.result

@@ -1273,10 +1273,10 @@ The following specify which files/extra groups are read (specified before remain
  application layer.If set to 0, system dependent default
  is used. (Automatically configured unless set explicitly)
  --tcp-keepalive-time=# 
- Timeout, in milliseconds, with no activity until the
- first TCP keep-alive packet is sent.If set to 0, system
- dependent default is used. (Automatically configured
- unless set explicitly)
+ Timeout, in seconds, with no activity until the first TCP
+ keep-alive packet is sent.If set to 0, system dependent
+ default is used. (Automatically configured unless set
+ explicitly)
  --thread-cache-size=# 
  How many threads we should keep in a cache for reuse.
  These are freed after 5 minutes of idle time

mysql-test/suite/sys_vars/r/sysvars_server_embedded.result

@@ -3335,7 +3335,7 @@ COMMAND_LINE_ARGUMENT	REQUIRED
 VARIABLE_NAME	TCP_KEEPALIVE_TIME
 VARIABLE_SCOPE	GLOBAL
 VARIABLE_TYPE	INT
-VARIABLE_COMMENT	Timeout, in milliseconds, with no activity until the first TCP keep-alive packet is sent.If set to 0, system dependent default is used.
+VARIABLE_COMMENT	Timeout, in seconds, with no activity until the first TCP keep-alive packet is sent.If set to 0, system dependent default is used.
 NUMERIC_MIN_VALUE	0
 NUMERIC_MAX_VALUE	2147483
 NUMERIC_BLOCK_SIZE	1

mysql-test/suite/sys_vars/r/sysvars_server_notembedded.result

@@ -4015,7 +4015,7 @@ COMMAND_LINE_ARGUMENT	REQUIRED
 VARIABLE_NAME	TCP_KEEPALIVE_TIME
 VARIABLE_SCOPE	GLOBAL
 VARIABLE_TYPE	INT
-VARIABLE_COMMENT	Timeout, in milliseconds, with no activity until the first TCP keep-alive packet is sent.If set to 0, system dependent default is used.
+VARIABLE_COMMENT	Timeout, in seconds, with no activity until the first TCP keep-alive packet is sent.If set to 0, system dependent default is used.
 NUMERIC_MIN_VALUE	0
 NUMERIC_MAX_VALUE	2147483
 NUMERIC_BLOCK_SIZE	1

sql/sys_vars.cc

@@ -5679,7 +5679,7 @@ vio_keepalive_opts opt_vio_keepalive;
 
 static Sys_var_int Sys_keepalive_time(
  "tcp_keepalive_time",
- "Timeout, in milliseconds, with no activity until the first TCP keep-alive packet is sent."
+ "Timeout, in seconds, with no activity until the first TCP keep-alive packet is sent."
  "If set to 0, system dependent default is used.",
  AUTO_SET GLOBAL_VAR(opt_vio_keepalive.idle),
  CMD_LINE(REQUIRED_ARG), VALID_RANGE(0, INT_MAX32/1000),