fr + gbproxy: Start to use AF_PACKET ENOBUFS work-around

If send() on AF_PACKET returns ENOBUFS, usleep for 2ms and re-try
until it succeeds.

Change-Id: Id7bdd2c690eae3bec1df7634944cd73f0bf0b29a
Closes: OS#5343
diff --git a/gbproxy/GBProxy_Tests.default b/gbproxy/GBProxy_Tests.default
index 8634b49..b0f28f5 100644
--- a/gbproxy/GBProxy_Tests.default
+++ b/gbproxy/GBProxy_Tests.default
@@ -21,6 +21,7 @@
 *.GBPVTY.CTRL_CLIENT_CLEANUP_LINEFEED := "yes"
 *.GBPVTY.CTRL_DETECT_CONNECTION_ESTABLISHMENT_RESULT := "yes"
 *.GBPVTY.PROMPT1 := "OsmoGbProxy> "
+*.FR.sleep_on_enobufs := "2000" # 2ms
 
 
 [MODULE_PARAMETERS]