rewrite srs channel estimation to fix memory alignment in SRS channel estimation

The memory alignment is required to use c16multaddVectRealComplex
in SRS channel interpolation. With a change in SRS comb_offset, the
existing algorithm was giving segmentation fault.

The existing srs channel estimation required memory alignment at two
stages. 1. When k = 0 (the first srs subcarrier), 2. When subcarrier <
K_TC (wrapped around after ofdm_symbol_size). Thus two memory alignments
are required leading to complications.

The srs channel estimation is now simplified to do it linearly instead of
wrapping around. This simplified the memory alignment required only when
k = 0.

openair1/SCHED_NR/phy_procedures_nr_gNB.c

@@ -938,7 +938,8 @@ void nr_srs_rx_procedures(PHY_VARS_gNB *gNB,
           T_INT(slot_rx),
           T_INT(ant_rx_ind),
           T_INT(p_ind),
-          T_BUFFER(srs_estimated_channel_time_shifted[ant_rx_ind][p_ind], ofdm_symbol_size * sizeof(c16_t)));
+          T_BUFFER(srs_estimated_channel_time_shifted[ant_rx_ind][p_ind],
+                   NR_SRS_IDFT_OVERSAMP_FACTOR * ofdm_symbol_size * sizeof(c16_t)));
       }
       noise_power_avg += noise_power;
     }