Add comments, conform to the kernel coding style
and add bounds checking in ISF import module.

Don't require WFID in ISF header and increase minimum
amount of bytes required to process the header.
Rename members of struct context to be more descriptive.

Don't perform header parsing until "CURVE#" (indicating
data section start) is found. This approach doesn't require
minimum header size. If a large amount of bytes has been loaded
and "CURVE#" still has not been found, an error code is returned.

Rename variables and make comments more descriptive.

First try to find "NR_PT" header item and then increase
the confidence if the file extension matches.
The extension comparison is performed ignoring
the case of the characters.

Use character values instead of numeric values
to obtain curve metadata.