Add "rtp-efr" format support for RTP payload according to RFC3551 4.5.9

The RTP EFR payload is a bit like the FR payload: one nibble magic
marker, then followed by the actual codec bits.  So we need to
add/remove that magic marker and shift the remainder by one nibble.
diff --git a/src/Makefile.am b/src/Makefile.am
index 07f1d51..c62e4e7 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -6,7 +6,7 @@
 
 COM_SOURCES = procqueue.c pq_file.c pq_format.c pq_codec.c pq_rtp.c pq_alsa.c \
 		formats.c fmt_amr.c fmt_gsm.c fmt_hr_ref.c fmt_racal.c \
-		fmt_amr_opencore.c fmt_rtp_amr.c fmt_rawpcm.c fmt_ti.c benchmark.c \
+		fmt_amr_opencore.c fmt_rtp_amr.c fmt_rtp_efr.c fmt_rawpcm.c fmt_ti.c benchmark.c \
 		codecs.c codec_pcm.c codec_hr.c codec_fr.c codec_efr.c codec_amr.c
 
 bin_PROGRAMS = gapk