Avoid truncated calculation of samples per frame on some 'odd' clock rates.

[nanang]

Sample cases:

1. On clock rate 11025, when ptime is set to 10ms, number of samples per frame will be 110.25 which will be truncated to 110.
2. When a port, which works on clock rate 11025Hz ptime 40ms (which is safe from truncation), is added to a conference bridge that works on clock rate 16000Hz ptime 10ms, the conference will need to resample a frame of 10ms from the port, which can cause truncation.

This may also happen in clock rate 22050Hz.

[nanang]

TeluuCon? 2018: only applicable to PCM