gst/rtp/: Add static payload numbers in addition to the dynamic ones.

gst/rtp/: Add static payload numbers in addition to the dynamic ones.

Original commit message from CVS:
Patch by: Ville Syrjala <ville dot syrjala at movial dot fi>
* gst/rtp/gstrtpgsmpay.c:
* gst/rtp/gstrtph263pay.c:
* gst/rtp/gstrtpmpapay.c:
* gst/rtp/gstrtppcmapay.c: (gst_rtp_pcma_pay_flush),
(gst_rtp_pcma_pay_handle_buffer):
* gst/rtp/gstrtppcmupay.c: (gst_rtp_pcmu_pay_flush):
Add static payload numbers in addition to the dynamic ones.
Fixes #361639.