vty: clarify EGPRS Packet Channel Request message support

According to 3GPP TS 44.060, section 12.24, GPRS Cell Options IE
contains two parameters related to 11 bit Access Burst support:

  - ACCESS_BURST_TYPE - whether the 8 or 11 bit format shall be
    used in the PACKET CHANNEL REQUEST message, the PTCCH/U block,
    PACKET CONTROL ACKNOWLEDGMENT and the PS HANDOVER ACCESS
    messages on the PRACH (if present).

  - EGPRS_PACKET_CHANNEL_REQUEST - whether EGPRS capable MSs shall
    use EGPRS PACKET CHANNEL REQUEST message for Uplink TBF
    establishment on the RACH or on the PRACH (if present).

The VTY option 'gprs 11bit_rach_support_for_egprs' actually controls
the second parameter - EGPRS_PACKET_CHANNEL_REQUEST, though it may
be hard to understand this from its name and description.

This patch is actually a group of tightly related changes:

  - deprecate 'gprs 11bit_rach_support_for_egprs (0|1)':
    - update its description to avoid any possible confusion,
    - print a warning if it's used in non-EGPRS mode,
    - print a warning if it's still used;

  - introduce '[no] gprs egprs-packet-channel-request':
    - ensure that it can only set / printed in the EGPRS mode;

  - take a chance to clean-up / rename the related struct members:
    - 'supports_egprs_11bit_rach' -> bool 'egprs_pkt_chan_request',
    - remove 'supports_egprs_11bit_rach' from 'gprs_cell_options'
      because we already have 'ext_info.use_egprs_p_ch_req' there.

Change-Id: Ied5bd10a806aeeac65ef32339d4ab0e3700e5da9
diff --git a/include/osmocom/bsc/gsm_data.h b/include/osmocom/bsc/gsm_data.h
index 2595174..9a1db07 100644
--- a/include/osmocom/bsc/gsm_data.h
+++ b/include/osmocom/bsc/gsm_data.h
@@ -1150,7 +1150,6 @@
 
 	/* Not entirely sure how ip.access specific this is */
 	struct {
-		uint8_t supports_egprs_11bit_rach;
 		enum bts_gprs_mode mode;
 		struct {
 			struct gsm_abis_mo mo;
@@ -1167,6 +1166,7 @@
 		uint8_t rac;
 		uint8_t net_ctrl_ord;
 		bool ctrl_ack_type_use_block;
+		bool egprs_pkt_chan_request;
 	} gprs;
 
 	/* threshold (in percent) when BTS shall send CCCH LOAD IND */
diff --git a/include/osmocom/bsc/rest_octets.h b/include/osmocom/bsc/rest_octets.h
index 2c1b162..7df66f7 100644
--- a/include/osmocom/bsc/rest_octets.h
+++ b/include/osmocom/bsc/rest_octets.h
@@ -82,7 +82,6 @@
 	uint32_t t3192;	/* in milliseconds */
 	uint32_t drx_timer_max;/* in seconds */
 	uint32_t bs_cv_max;
-	uint8_t  supports_egprs_11bit_rach;
 	bool ctrl_ack_type_use_block; /* use PACKET CONTROL ACKNOWLEDGMENT */
 
 	uint8_t ext_info_present;