Limit length of SSID input string to 32

Limits the UI text box of the SSID field to 32 characters (which is
standard) from previously being unlimited in the UI but constrained
in the driver implementation.

See IEEE 802.11-1999 7.3.2.1 Service Set Identity (SSID) element.

Change-Id: I17573ee338ed744a2bc0258ee2c0f382c1a5c931