sockaddr_str: add conversion to,from osmo_sockaddr

Add functions to pass struct osmo_sockaddr to the
osmo_sockaddr_str_{to,from}* API directly.

So far the interface to osmo_sockaddr_str_ is:

  osmo_sockaddr_str_from_sockaddr(&my_sa_str, &my_osa->u.sas);

I'm working a lot with osmo_sockaddr at the moment, and the cumulated
time of forgetting to add 'u.sas' and having another compilation cycle
because of those is justifying this additional API.

Change-Id: I0df84b4bb8cb5d8434b735fa3a38e7f95be43e91
diff --git a/TODO-RELEASE b/TODO-RELEASE
index 01f7c41..ce04162 100644
--- a/TODO-RELEASE
+++ b/TODO-RELEASE
@@ -11,6 +11,7 @@
 core      ADD       osmo_sock_multiaddr_get_ip_and_port(), osmo_multiaddr_ip_and_port_snprintf(), osmo_sock_multiaddr_get_name_buf()
 core      ADD       osmo_sock_sctp_get_peer_addr_info()
 core      ADD       gsmtap_inst_fd2() core, DEPRECATE gsmtap_inst_fd()
+core      ADD       osmo_sockaddr_str_from_osa() osmo_sockaddr_str_to_osa()
 core		behavior change		osmo_tdef_fsm_inst_state_chg(): allow millisecond precision
 core		ABI change		osmo_io_ops now contains a struct of structs, not union of structs
 core		ABI change		osmo_iofd_set_ioops() now returns a value (error code)