Changes

E1: support HRv1 codec on both 16k and 8k subslots

HRv1 support in OsmoMGW-E1 was previously broken (couldn't work
on either 16k or 8k subslots) because of inconsistency: the TRAU
frame type was set to OSMO_TRAU16_FT_HR, but the TRAU sync pattern
was set to OSMO_TRAU_SYNCP_8_HR.  However, now that libosmotrau
has proper support for HRv1 TRAU frame encoding and RTP conversion
in both 16k and 8k formats, drive it correctly in OsmoMGW-E1.

While at it, change the code structure to avoid else-after-return.
Was the original code written and merged in a time before strict
linter checks?

Change-Id: Ifadbdc68905178c6ffdd673a6fb71c18610c9847