add osmo_sockaddr_to_str_and_uint()

This came from osmo-bsc refactoring patch I82e3f918295daa83274a4cf803f046979f284366
https://gerrit.osmocom.org/#/c/osmo-bsc/+/9671/6/src/osmo-bsc/gsm_data.c@1708

Add regression test in utils_test.c.

Change-Id: I1f2918418c38918c5ac70acaa51a47adfca12b5e
diff --git a/include/osmocom/core/socket.h b/include/osmocom/core/socket.h
index 47d9f30..20515b9 100644
--- a/include/osmocom/core/socket.h
+++ b/include/osmocom/core/socket.h
@@ -44,6 +44,9 @@
 
 int osmo_sockaddr_is_local(struct sockaddr *addr, unsigned int addrlen);
 
+unsigned int osmo_sockaddr_to_str_and_uint(char *addr, unsigned int addr_len, uint16_t *port,
+					   const struct sockaddr *sa);
+
 int osmo_sock_unix_init(uint16_t type, uint8_t proto,
 			const char *socket_path, unsigned int flags);