Move pdp_get_peer_ipv() to lib/util.*

Preparation for next commit, where this function will be needed inside
libmisc (lib/*).

Change-Id: Ibab4f6c09d1e5f0e9cfaea28ae1e7ab5b5c219b5
diff --git a/lib/util.c b/lib/util.c
new file mode 100644
index 0000000..6bb0d85
--- /dev/null
+++ b/lib/util.c
@@ -0,0 +1,35 @@
+/*
+ * misc helpers
+ * Copyright 2019 sysmocom - s.f.m.c. GmbH <info@sysmocom.de>
+ *
+ * The contents of this file may be used under the terms of the GNU
+ * General Public License Version 2, provided that the above copyright
+ * notice and this permission notice is included in all copies or
+ * substantial portions of the software.
+ *
+ */
+
+#include "../gtp/pdp.h"
+
+#include "ippool.h"
+#include "in46_addr.h"
+
+/*! Get the peer of pdp based on IP version used.
+*  \param[in] pdp PDP context to select the peer from.
+*  \param[in] v4v6 IP version to select. Valid values are 4 and 6.
+*  \returns The selected peer matching the given IP version. NULL if not present.
+*/
+struct ippoolm_t *pdp_get_peer_ipv(struct pdp_t *pdp, bool is_ipv6) {
+	uint8_t i;
+
+	for (i = 0; i < 2; i++) {
+		struct ippoolm_t * ippool = pdp->peer[i];
+		if (!ippool)
+			continue;
+		if (is_ipv6 && in46a_is_v6(&ippool->addr))
+			return ippool;
+		else if (!is_ipv6 && in46a_is_v4(&ippool->addr))
+			return ippool;
+	}
+	return NULL;
+}