stats: use correct IANA registry for SRTP cipher

which incorrect used the SDES registry, i.e.
  AES_CM_128_HMAC_SHA1_80
instead of the DTLS-SRTP registry, i.e.
  SRTP_AES128_CM_HMAC_SHA1_80
et al.

Note: this is technically a breaking change.

PSA: https://groups.google.com/g/discuss-webrtc/c/bEWMKetC40U
Bug: webrtc:518266748
Change-Id: I6040c576aea993b56cf4033e9c7ff622bbbc9e36
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/477381
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Reviewed-by: Guido Urdaneta <guidou@webrtc.org>
Commit-Queue: Philipp Hancke <philipp.hancke@googlemail.com>
Cr-Commit-Position: refs/heads/main@{#47982}