Add genl_socket_close() function

We've had genl_socket_open() but no corresponding genl_socket_close()
so far.  Let's fix that.
diff --git a/TODO-RELEASE b/TODO-RELEASE
new file mode 100644
index 0000000..24da897
--- /dev/null
+++ b/TODO-RELEASE
@@ -0,0 +1 @@
+* new genl_socket_close() function
diff --git a/include/libgtpnl/gtpnl.h b/include/libgtpnl/gtpnl.h
index 33bb275..6cd9f46 100644
--- a/include/libgtpnl/gtpnl.h
+++ b/include/libgtpnl/gtpnl.h
@@ -7,6 +7,7 @@
 struct nlmsghdr;
 
 struct mnl_socket *genl_socket_open(void);
+void genl_socket_close(struct mnl_socket *nl);
 struct nlmsghdr *genl_nlmsg_build_hdr(char *buf, uint16_t type, uint16_t flags,
 				      uint32_t seq, uint8_t cmd);
 int genl_socket_talk(struct mnl_socket *nl, struct nlmsghdr *nlh, uint32_t seq,
diff --git a/src/genl.c b/src/genl.c
index 311480c..f534221 100644
--- a/src/genl.c
+++ b/src/genl.c
@@ -106,6 +106,12 @@
 }
 EXPORT_SYMBOL(genl_socket_open);
 
+void genl_socket_close(struct mnl_socket *nl)
+{
+	mnl_socket_close(nl);
+}
+EXPORT_SYMBOL(genl_socket_close);
+
 int genl_socket_talk(struct mnl_socket *nl, struct nlmsghdr *nlh, uint32_t seq,
 		     int (*cb)(const struct nlmsghdr *nlh, void *data),
 		     void *data)
diff --git a/src/libgtpnl.map b/src/libgtpnl.map
index 9ce465d..804f8b3 100644
--- a/src/libgtpnl.map
+++ b/src/libgtpnl.map
@@ -1,6 +1,7 @@
 LIBGTPNL_1.0 {
 global:
   genl_socket_open;
+  genl_socket_close;
   genl_nlmsg_build_hdr;
   genl_socket_talk;
   genl_lookup_family;