Link orchagent against jemalloc (sonic-net#3473)

What I did
Force orchagent to use jemalloc instead of the standard glibc malloc implementation.

Why I did it
Glibc's malloc implementation can result in memory fragmentation which prevents orchagent from returning freed memory to the kernel - this results in excessively high memory utilization.

orchagent/Makefile.am

@@ -138,7 +138,7 @@ orchagent_SOURCES += p4orch/p4orch.cpp \
 
 orchagent_CFLAGS = $(DBGFLAGS) $(AM_CFLAGS) $(CFLAGS_COMMON) $(CFLAGS_SAI) $(CFLAGS_ASAN)
 orchagent_CPPFLAGS = $(DBGFLAGS) $(AM_CFLAGS) $(CFLAGS_COMMON) $(CFLAGS_SAI) $(CFLAGS_ASAN)
-orchagent_LDADD = $(LDFLAGS_ASAN) -lnl-3 -lnl-route-3 -lpthread -lsairedis -lsaimeta -lsaimetadata -lswsscommon -lzmq -lprotobuf -ldashapi
+orchagent_LDADD = $(LDFLAGS_ASAN) -lnl-3 -lnl-route-3 -lpthread -lsairedis -lsaimeta -lsaimetadata -lswsscommon -lzmq -lprotobuf -ldashapi -ljemalloc
 
 routeresync_SOURCES = routeresync.cpp
 routeresync_CFLAGS = $(DBGFLAGS) $(AM_CFLAGS) $(CFLAGS_COMMON) $(CFLAGS_ASAN)