llc: Add CoDel AQM implementation

This commit adds an implementation of the CoDel algorithm based on
the reference pseudocode presented in
http://queue.acm.org/appendices/codel.html. Instead of abstracting
the queue itself, the implementation provides a time stamp based
automaton which is invoked after a package has been dequeued.

Note that the modifications of the algorithm shown in
https://tools.ietf.org/html/draft-ietf-aqm-codel-01 are not yet
applied.

Sponsored-by: On-Waves ehf
diff --git a/src/Makefile.am b/src/Makefile.am
index a63281f..3587416 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -54,7 +54,8 @@
 	sba.cpp \
 	decoding.cpp \
 	llc.cpp \
-	rlc.cpp
+	rlc.cpp \
+	gprs_codel.c
 
 if ENABLE_SYSMOBTS
 libgprs_la_SOURCES += \
@@ -99,7 +100,8 @@
 	decoding.h \
 	llc.h \
 	pcu_utils.h \
-	cxx_linuxlist.h
+	cxx_linuxlist.h \
+	gprs_codel.h
 
 osmo_pcu_SOURCES = pcu_main.cpp