* fix: keep GnuTLS and NSS probing enabled by default in sslsniff
Commit 337af70 (add hook of ssl_ex version) flipped the default provider
flags to off. The --no-gnutls and --no-nss options only clear the same
flags, so GnuTLS and NSS probing became unreachable and the documented
default behavior (sniff OpenSSL and GnuTLS functions) stopped holding.
Restore the gnutls/nss defaults to on, and warn instead of attaching
against a NULL library path when a provider library is not present on
the system.
* docs: sync lesson 30 provider-attach excerpt with sslsniff source
Update the lesson-30 README code excerpts (English and Chinese) to the
current sslsniff.c provider-attach block, which now warns and skips a
provider whose library is not present instead of attaching against a
NULL path.
* fix: match SSL library names literally
* fix: retain all sslsniff provider links
* refactor: centralize sslsniff provider setup
* refactor: keep provider branches out of main
110b91f873