When copying attributes, the len argument was padded out and the
resulting memcpy() would copy beyond the end of the source buffer.
Avoid this, and use size_t for val_len to avoid all the casts.
Similarly, avoid source buffer casts and use void *.

Additionally enforces val_len can be represented by u16 and that the DMA
buffer was not overflowed. Fixes the size of mfa, which is not
FC_FDMI_PORT_ATTR_MAXFRAMESIZE_LEN (but it will be padded up to 4). This
was noticed by the future CONFIG_FORTIFY_SOURCE checks.

Cc: Daniel Micay <danielmicay@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Varun Prakash <varun@chelsio.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>