libtimeinstate: initialize current freq before starting tracking

Currently, our BPF programs start with no knowledge of current CPU
frequency and tracking cannot begin for a cluster until a frequency
transition happens & makes this information available. On cuttlefish,
CPU frequency never changes, so tracking never starts & cuttlefish
can't be used for testing this feature.
To resolve this, pass the BPF programs initial frequency information
read from the scaling_cur_freq sysfs nodes.

Test: libtimeinstate_test passes on cuttlefish
Test: confirm that uid_time_in_state BPF map contains data on
cuttlefish
Bug: 138317993
Signed-off-by: Connor O'Brien <connoro@google.com>

Change-Id: I5b24c1311e1b58b73c7e32f41c2d99c5ab344549