schannel: Don't reset recv/send function pointers on renegotiation

[JDepooter]

Fixes #9451

These function pointers will have been set when the initial TLS handshake was completed. If they are unchanged, there is no need to set them again. If they have been changed, as is the case with HTTP/2, we don't want to override that change. That would result in the http2_recv/send functions being completely bypassed.

It should be investigated whether the same change should be made to the other TLS backends. They don't seem to have the same amount of renegotiation logic that SChannel does. It appears that OpenSSL/BoringSSL may outright forbid TLS renegotiation.

[bagder]

./vtls/schannel.c:1939:5: warning: badly placed open brace (BRACEPOS)
     {
     ^

[JDepooter]

./vtls/schannel.c:1939:5: warning: badly placed open brace (BRACEPOS)
     {
     ^

Sorry, forgot to check formatting. I've pushed a new commit fixing this.

[jay]

Thanks!