Use MSG_MORE instead of 2 setsockopt calls on every AsyncSSLSocket write.

Use MSG_MORE instead of 2 setsockopt calls on every AsyncSSLSocket write.

Summary: Previously we set the cork option on the socket before making multiple writes, and then unset it after, which elip found was hurting perf with 2 extra syscalls. The cork logic was also not the same as the buffer combining logic, which made us often set cork even when only doing one write.

Reviewed By: djwatson

Differential Revision: D4058357

fbshipit-source-id: 1a07447ff5e027751e455a2403e0042bf67cb1c5