streamzap uses 'struct timeval' to store the start time of a signal for
gap tracking. struct timeval uses a 32-bit seconds representation which
will overflow in year 2038 and beyond. Replace struct timeval with ktime_t
which uses a 64-bit seconds representation and is 2038 safe. This patch
uses ktime_get_real() preserving the use of wall-clock time in the
original code.