Correct SQL Anywhere driver default port to 2638

It looks like this was a simple typo. 

References:
SQLA16 - http://dcx.sybase.com/index.html#sa160/en/dbadmin/serverport-network-conparm.html
SQLA12 - http://infocenter.sybase.com/help/index.jsp?topic=/com.sybase.help.sqlanywhere.11.0.1/dbadmin_en11/serverport-network-conparm.html

It probably wasn't noticed immediately due to the fact SQL Anywhere drivers cache database server address information in a file on disk (sasrv.ini). Once the cache is populated with the database name, it's possible to connect successfully even if the port you were specifying in your code was incorrect (like 2683). 

http://dcx.sybase.com/1201/en/dbadmin/servernamecaching.html