snic: correctly check for array overrun on overly long version number

The snic version number is expected to be 4 decimals in the form like a
netmask string with each number stored in an element in array v.
However, there is an off-by-one check on the number of elements in v
allowing one to pass a 5 decimal version number causing v[4] to be
referenced, causing a buffer overrun.  Fix the off-by-one error by
comparing to i > 3 rather than 4.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: Shane Seymour <shane.seymour@hpe.com>
Reviewed-by: Ewan Milne <emilne@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>