Always tag SRTP_PROTECTION_PROFILE and BIO_METHOD as const.

The BIO_METHODs ought to be const so they can go into rodata; BoringSSL makes
BIO_new take a const BIO_METHOD *, so there's no need for it to be non-const.
Also set SRTP_PROTECTION_PROFILE as const so we can constify those within
BoringSSL (https://boringssl-review.googlesource.com/#/c/2720/)

BUG=none
R=henrike@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/34649004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@8013 4adac7df-926f-26a2-2b94-8c16560cd09d
2 files changed