vty: Add 'show ms all' command

This command lists the entries of the ms_store by a line per MS.
Beside TLLI and IMSI, some measurement and state information is
shown.

A ms_list() getter method is added to GprsMsStorage to obtain a list
of the MsGprs objects.

The following VTY command is added to the 'enable' node:

 - show ms all

Sponsored-by: On-Waves ehf
diff --git a/src/gprs_ms_storage.h b/src/gprs_ms_storage.h
index 3552602..ad1e656 100644
--- a/src/gprs_ms_storage.h
+++ b/src/gprs_ms_storage.h
@@ -39,6 +39,7 @@
 	GprsMs *get_ms(uint32_t tlli, uint32_t old_tlli = 0, const char *imsi = 0) const;
 	GprsMs *create_ms(uint32_t tlli, enum gprs_rlcmac_tbf_direction dir);
 
+	const LListHead<GprsMs>& ms_list() const {return m_list;}
 private:
 	BTS *m_bts;
 	LListHead<GprsMs> m_list;