gst/law/: Make negotiation a bit modern.

gst/law/: Make negotiation a bit modern.

Original commit message from CVS:
Based on patch by: mersad <mersad at axis dot com>
* gst/law/alaw-decode.c: (gst_alaw_dec_sink_setcaps),
(gst_alaw_dec_chain), (gst_alaw_dec_change_state):
* gst/law/alaw-decode.h:
* gst/law/alaw-encode.c: (gst_alaw_enc_chain):
* gst/law/mulaw-decode.c: (mulawdec_sink_setcaps),
(gst_mulawdec_chain), (gst_mulawdec_change_state):
* gst/law/mulaw-decode.h:
* gst/law/mulaw-encode.c: (gst_mulawenc_chain):
Make negotiation a bit modern.
Use pad_alloc. Fixes #525359.