NR RRC/SDAP: enable SDAP by default and update CI/docs

- Change gNB RRC enable_sdap default to true
- Update RRC and RUNMODEM docs to reflect new default behavior
- Clean up CI gNB configs by removing redundant enable_sdap=1
- Keep explicit SDAP disable config for NFAPI gNB VNF

doc/RRC/rrc-usage.md

@@ -84,7 +84,7 @@ the [MAC configuration](../MAC/mac-usage.md) as well for SIB configuration.
       `0xffffff` is a reserved value and means "no SD"
     Note that: SST=1, no SD is "eMBB"; SST=2, no SD is "URLLC"; SST=3, no SD
     is "mMTC"
-- `enable_sdap` (default: false): enable the use of the SDAP layer. If
+- `enable_sdap` (default: true): enable the use of the SDAP layer. If
   deactivated, a transparent SDAP header is prepended to packets, but no
   further processing is being done.
 - `cu_sibs` (default: `[]`) list of SIBs to give to the DU for transmission.

doc/RUNMODEM.md

@@ -544,7 +544,7 @@ sudo ./nr-uesoftmodem --do-ra
 
 #### Run OAI with SDAP & Custom DRBs
 
-To run OAI gNB with SDAP, simply include `--gNBs.[0].enable_sdap 1` to the binary's arguments.
+SDAP is enabled by default. To disable SDAP, include `--gNBs.[0].enable_sdap 0` to the binary's arguments.
 
 The DRB creation is dependent on the 5QI. 
 If the 5QI corresponds to a GBR Flow it assigns a dedicated data radio bearer.