Make EARFCN size calculation more robust

* add osmo_earfcn_bit_size_ext() function which allows to specify how many
  EARFCNs we should skip when estimating required bit size for SI2quater
* make old osmo_earfcn_bit_size() into wrapper over newly added function
  and mark it as deprecated

This is necessary to properly estimate necessary space for EARFCNs when
they are spread over several SI2q messages with different index.

Change-Id: I92e12e91605bdab9916a3f665705287572434f74
Related: RT#8792
diff --git a/src/gsm/libosmogsm.map b/src/gsm/libosmogsm.map
index 97fd2b4..8fb9878 100644
--- a/src/gsm/libosmogsm.map
+++ b/src/gsm/libosmogsm.map
@@ -48,6 +48,7 @@
 osmo_earfcn_add;
 osmo_earfcn_del;
 osmo_earfcn_bit_size;
+osmo_earfcn_bit_size_ext;
 osmo_earfcn_init;
 
 gprs_cipher_gen_input_i;