Correct field sizes for PGN 126996: Product Information

Software Version Code and Model Version should both be 32 bytes.

Example before and after from four devices on my workbench:

#### Before
```
2014-08-14-22:06:14.091 6   0 255 126996 Product Information:  NMEA 2000 Version = 1300; Product Code = 28199; Model ID = NMEA 2000 PC Interface (NGT-1); Software Version Code = 1.100, 2.210NGT-1-US; Model Version = B  hv1.03; Model Serial Code = 110737; Certification Level = 0; Load Equivalency = 1
2014-08-14-22:06:14.113 6  10 255 126996 Product Information:  NMEA 2000 Version = 1301; Product Code = 29971; Model ID = MS700; Software Version Code = 1.01.18                         FUSION-L; Model Version = INK-1.0; Model Serial Code = 1692; Certification Level = 1; Load Equivalency = 1
2014-08-14-22:06:14.126 6  88 255 126996 Product Information:  NMEA 2000 Version = 1301; Product Code = 21703; Model ID = FPM100; Software Version Code = 1.0.11.0; Model Version = ; Model Serial Code = 1640296; Certification Level = 0; Load Equivalency = 8
2014-08-14-22:06:14.138 6 128 255 126996 Product Information:  NMEA 2000 Version = 1210; Product Code = 5973; Model ID = WSO100; Software Version Code = 2.0.132.0; Model Version = ; Model Serial Code = 1201861; Certification Level = 0; Load Equivalency = 3
```
#### After
```
2014-08-14-22:07:20.481 6   0 255 126996 Product Information:  NMEA 2000 Version = 1300; Product Code = 28199; Model ID = NMEA 2000 PC Interface (NGT-1); Software Version Code = 1.100, 2.210; Model Version = NGT-1-USB  hv1.03; Model Serial Code = 110737; Certification Level = 0; Load Equivalency = 1
2014-08-14-22:07:20.504 6  10 255 126996 Product Information:  NMEA 2000 Version = 1301; Product Code = 29971; Model ID = MS700; Software Version Code = 1.01.18; Model Version = FUSION-LINK-1.0; Model Serial Code = 1692; Certification Level = 1; Load Equivalency = 1
2014-08-14-22:07:20.517 6  88 255 126996 Product Information:  NMEA 2000 Version = 1301; Product Code = 21703; Model ID = FPM100; Software Version Code = 1.0.1; Model Version = 1.0; Model Serial Code = 1640296; Certification Level = 0; Load Equivalency = 8
2014-08-14-22:07:20.528 6 128 255 126996 Product Information:  NMEA 2000 Version = 1210; Product Code = 5973; Model ID = WSO100; Software Version Code = 2.0.13; Model Version = 2.0; Model Serial Code = 1201861; Certification Level = 0; Load Equivalency = 3
```