coding: fix bit ordering in 11-bit RACH coding functions

According to 3GPP TS 44.004, figure 7.4a.b, the format of 11-bit
RACH uplink / Uplink access burst block is as defined follows:

  <---------------------------------------------------

      8     7     6     5     4     3     2     1
  +--------------------------------------------------+
  |  11 bit RACH uplink / Uplink access burst block  | OCT1
  +--------------------------------------------------+
                                 |                   | OCT2
                                 +-------------------+

As was (correctly) assumed in [1], the bit ordering in 11-bit RACH
coding functions is wrong. The problem is that neither of generic
functions from bit16gen.h can be used to load / store the RA11
value (regardless of the endianness), because they assume that
the payload is 16 bit long.

With this patch applied, RA11 values from [1] look correct:

  < EGPRS Packet channel request message content > ::=
    < Signalling : 110011  < RandomBits : 00111 > > |
    < Signalling : 110011  < RandomBits : 00110 > > |
    < Signalling : 110011  < RandomBits : 01111 > > |
    < Signalling : 110011  < RandomBits : 01100 > > |
    < Signalling : 110011  < RandomBits : 00111 > > |
    < Signalling : 110011  < RandomBits : 10110 > > ;

[1] Id80e471d252b9416217b56f4c8c0a8f5f1289fee

Change-Id: I43d30611dd69f77f2b3b46f4b56056a8891d3c24
Related: OS#1548
diff --git a/tests/coding/coding_test.ok b/tests/coding/coding_test.ok
index 496ce89..3a4fbf2 100644
--- a/tests/coding/coding_test.ok
+++ b/tests/coding/coding_test.ok
@@ -40,12 +40,12 @@
 Decoded: 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13 14 15 16 17 
 xcch_decode: n_errors=60 n_bits_total=456 ber=0.13
 
-Decoded RA11: 0x7cc
-Decoded RA11: 0x6cc
-Decoded RA11: 0x7cd
-Decoded RA11: 0x4cd
-Decoded RA11: 0x7cc
-Decoded RA11: 0x6ce
+Decoded RA11: 0x667
+Decoded RA11: 0x666
+Decoded RA11: 0x66f
+Decoded RA11: 0x66c
+Decoded RA11: 0x667
+Decoded RA11: 0x676
 
 Encoding: 03 03 01 00 
 U-Bits: 111001110011000011100111001100001101001111000000000011010000011010110111111100