net/http: update bundled http2
net/http: update bundled http2

Updates x/net/http2 to git rev ef2e00e88 for https://golang.org/cl/24560,
"http2: make Transport return server's GOAWAY error back to the user"

Fixes #14627

Change-Id: I2bb123a3041e168db7c9446beef4ee47638f17ee
Reviewed-on: https://go-review.googlesource.com/24561
Reviewed-by: Andrew Gerrand <395a7d33bec8475c9b83b7d440f141bcbd994aa5@golang.org>
Run-TryBot: Andrew Gerrand <395a7d33bec8475c9b83b7d440f141bcbd994aa5@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

Cofyc/go,vsekhar/elastic-go,codestation/go,ImJasonH/go,Cofyc/go,polyverse-security/go,linux-on-ibm-z/go,nawawi/go,nawawi/go,derekmarcotte/go,golang/go,akutz/go,polyverse-security/go,golang/go,ImJasonH/go,akutz/go,akutz/go,nawawi/go,suncycheng/go,4ad/go,suncycheng/go,suncycheng/go,goodlang/good,CAFxX/go,linux-on-ibm-z/go,cloudflare/go,CAFxX/go,momchil-velikov/go,josharian/go,derekmarcotte/go,nawawi/go,CAFxX/go,codestation/go,vsekhar/elastic-go,Cofyc/go,polyverse-security/go,golang/go,momchil-velikov/go,akutz/go,Cofyc/go,CAFxX/go,4ad/go,christopher-henderson/Go,cloudflare/go,Cofyc/go,momchil-velikov/go,goodlang/good,CAFxX/go,golang/go,suncycheng/go,ImJasonH/go,cloudflare/go,goodlang/good,josharian/go,4ad/go,4ad/go,ImJasonH/go,CAFxX/go,ImJasonH/go,derekmarcotte/go,vsekhar/elastic-go,4ad/go,linux-on-ibm-z/go,suncycheng/go,nawawi/go,polyverse-security/go,codestation/go,vsekhar/elastic-go,goodlang/good,goodlang/good,CAFxX/go,vsekhar/elastic-go,linux-on-ibm-z/go,derekmarcotte/go,momchil-velikov/go,cloudflare/go,linux-on-ibm-z/go,derekmarcotte/go,Cofyc/go,momchil-velikov/go,goodlang/good,suncycheng/go,akutz/go,linux-on-ibm-z/go,golang/go,polyverse-security/go,ImJasonH/go,akutz/go,Cofyc/go,codestation/go,ImJasonH/go,derekmarcotte/go,cloudflare/go,derekmarcotte/go,momchil-velikov/go,vsekhar/elastic-go,akutz/go,josharian/go,golang/go,cloudflare/go,nawawi/go,josharian/go,CAFxX/go,josharian/go,4ad/go,ImJasonH/go,codestation/go,golang/go,polyverse-security/go,polyverse-security/go,josharian/go,josharian/go,suncycheng/go,codestation/go,vsekhar/elastic-go,nawawi/go,golang/go,momchil-velikov/go,akutz/go,cloudflare/go,derekmarcotte/go,vsekhar/elastic-go,4ad/go,codestation/go,linux-on-ibm-z/go,cloudflare/go,goodlang/good,momchil-velikov/go,codestation/go,Cofyc/go,linux-on-ibm-z/go,nawawi/go,josharian/go,goodlang/good,4ad/go,polyverse-security/go,suncycheng/go