Only pass -P for socket connection when port option is specified

[leonyu]

This fix implementation of be1f4b4 for GCP cloud-sql-proxy. cloud-sql-proxy creates multiple sockets on localhost pointing to multiple remote instances with default port.

$ curl -L http://mysqltuner.pl/ -o mysqltuner.pl
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0
  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0
100  254k  100  254k    0     0   524k      0 --:--:-- --:--:-- --:--:--  524k
$ MYSQL_PWD="[REDACTED]" ./mysqltuner.pl --socket=/cloudsql/[REDACTED] --user $USER --skippassword --forcemem 245760 --forceswap 0
 >>  MySQLTuner 2.2.12
	 * Jean-Marie Renouard <[email protected]>
	 * Major Hayden <[email protected]>
 >>  Bug reports, feature requests, and downloads at http://mysqltuner.pl/
 >>  Run with '--help' for additional options and output filtering

[--] Skipped version check for MySQLTuner script
[!!] Attempted to use login credentials, but they were invalid
exit 1
$ curl -LO https://raw.githubusercontent.com/leonyu/MySQLTuner-perl/master/mysqltuner.pl
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100  254k  100  254k    0     0  2973k      0 --:--:-- --:--:-- --:--:-- 2999k
$ MYSQL_PWD="[REDACTED]" ./mysqltuner.pl --socket=/cloudsql/[REDACTED] --user $USER --skippassword --forcemem 245760 --forceswap 0
 >>  MySQLTuner 2.2.12
	 * Jean-Marie Renouard <[email protected]>
	 * Major Hayden <[email protected]>
 >>  Bug reports, feature requests, and downloads at http://mysqltuner.pl/
 >>  Run with '--help' for additional options and output filtering

[--] Skipped version check for MySQLTuner script
[OK] Logged in using credentials passed on the command line
[--] Assuming 245760 MB of physical memory
[!!] Assuming 0 MB of swap space (use --forceswap to specify)
[OK] Operating on 64-bit architecture

-------- Storage Engine Statistics -----------------------------------------------------------------
...

[leonyu]

@i5513 please take a look as well

[jmrenouard]

Thanks @leonyu