C2SoftOpusEnc: Populate skip_samples in OpusHeader

skip_samples in opusHeader is now populated to signal codec delay
Without this, an ogg file created from this encoders output resulted
in codec delay being set to zero when it was played out in Android.

Test: Encode raw file to Opus -> Mux to Ogg -> Extract and decode
Test: Verify codec delay in decode step
Test: atest android.media.cts.EncoderTest#testOpusEncoders
Bug: 133506289

Change-Id: I05aeb909abf8b3fa62e709a099f5e544a7aa555c