Make TWT wake interval type as long

As the TWT Wake Interval Mantissa is a 2-byte field and TWT Wake
Interval Exponent is a 5-bit field, Maximum TWT Wake Interval =
65,535 x [2^31] microseconds. So make TWT wake inteval field type as
long to avoid overflow.

Bug: 296108122
Test: m
Change-Id: Id77cd094ae0601839de7f01994072d50ec39cd56