This should fix the cppcheck warning "The unsigned expression
'sizeof(struct _PKT_INFO)' will never be negative so it is either
pointless or an error to check if it is."
wmem_safe_mult() was only used to do an overflow-safe multiplication of
a type size and a count of elements of that type; replace it with
wmem_safe_mult_type_size(), which takes the type as the first argument,
and checks only whether the count of elements is <= 0.
