l1sap: fix gsmtap_ph_rach(): properly pack 8-bit and 11-bit RA
l1sap: fix gsmtap_ph_rach(): properly pack 8-bit and 11-bit RA

According to 3GPP TS 44.004, section 7.4a, two alternative RACH
block formats are specified: 8 bit (1 octet) and 11 bit. The
bit order is little-endian (right to left).

In L1SAP PH-RACH.ind structure (see ph_rach_ind_param) we use
a field of type uint16_t to store RA values regardles of the
block format. Thus when packing it to bytes, we cannot just
cast uint16_t* to uint8_t*, we need to do some bit shifting.

Change-Id: I0e91d825bb2e1897647dd5403c311d833a89ff2e

osmocom/osmo-bts,osmocom/osmo-bts,osmocom/osmo-bts