gNB: modify RLC configuration applied for SRB1 during RRCReestablishment

Thomas Schlichterrequested to merge
fix_NR_RLC_Config_during_RRCReestablishment into develop

TS 38.331 clause 5.3.7.4 specifies to apply the configuration defined in 9.2.1 for SRB1 at UE side. This implies that the gNB also has to apply sn_field_length = 12, but there are no implications on the other RLC parameters.

As wrong timer values break SRB1 e.g. for long RTT NTN scenarios, this commit switches to using the RLC timer values provided in the configuration file. Currently we still set poll_pdu, poll_byte and max_retx_threshold to the values defined in 9.2.1, but this can be changed.

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