net.c: add missing static.

Pointed out during code review of the recent refactor.
diff --git a/lib/net.c b/lib/net.c
index be69c9a..0235444 100644
--- a/lib/net.c
+++ b/lib/net.c
@@ -37,7 +37,7 @@
   return ai;
 }
 
-int xconnbind(struct addrinfo *ai_arg, int dobind)
+static int xconnbind(struct addrinfo *ai_arg, int dobind)
 {
   struct addrinfo *ai;
   int fd = -1, one = 1;