socket: Support setsokopt SCTP_INITMSG in osmo_sock_init2_multiaddr2()

This allows setting several socket paramets which can only be set before
SCTP INIT phase (connect()).

Since no release with osmo_sock_init2_multiaddr2() happened yet, we are
allowed to extend struct osmo_sock_init2_multiaddr_pars without bumping
the version field.

Related: SYS#6558
Change-Id: Ibc55932d954279927d1e70ccce1e8bf32b180d44
diff --git a/include/osmocom/core/socket.h b/include/osmocom/core/socket.h
index ba986f8..bbf828f 100644
--- a/include/osmocom/core/socket.h
+++ b/include/osmocom/core/socket.h
@@ -130,6 +130,18 @@
 				bool abort_on_failure;
 				uint32_t value;
 			} sockopt_asconf_supported;
+			struct {
+				bool set;
+				bool abort_on_failure;
+				bool num_ostreams_present;
+				bool max_instreams_present;
+				bool max_attempts_present;
+				bool max_init_timeo_present;
+				uint16_t num_ostreams_value;
+				uint16_t max_instreams_value;
+				uint16_t max_attempts_value;
+				uint16_t max_init_timeo_value;
+			} sockopt_initmsg;
 		} sctp;
 	};
 };