Setting default codec parameter issues (thanks Arie Velthoen for the report)

[nanang]

The original report can be found ​here.

Issues reported:

• codec description pool in codec manager is released before the new setting is copied, this causes problem when the new setting contains data (e.g: fmtp strings) that is allocated using that pool,
• dec_fmtp is copied twice, one of them should be enc_fmtp instead.

[nanang]

(In [3380]) Fix #1171, fixed issues in pjmedia_codec_mgr_set_default_param():

• updated the releasing of the old pool to be done after the new codec param is copied
• fixed the double dec_fmtp copy loop, one of them should be enc_fmtp copy loop instead