Changes

csd_v110: properly set bit E2 for TCH/F4.8 NT

As was reported by Mychaela Falconia in:

https://www.freecalypso.org/pipermail/community/2024-September/000941.html

contrary to 3GPP TS 48.020 Table 7, bit E2 is currently always 0
in the RTP output for TCH/F4.8 channels in non-transparent CSD mode.

The problem is that `desc->num_blocks` is 2 for TCH/F4.8 NT, so the
for-loop in csd_v110_rtp_encode() will iterate only 2 (not 4) times,
and thus `(i >> 1) & 0x01` never evaluates to 1 in this mode.

According to 3GPP TS 44.021, Figure 1, bit E7 is set to 0 in every
4-th frame (Q1), so use it to calculate the value of bit E2 properly.

Change-Id: If8307a9ce0fdc6da45157149ccef7b840ff9d9b3
Fixes: 183c08886 "csd_v110: properly set E1/E2/E3 for non-transparent data"
Related: OS#1572