libceph: update outdated comment in ceph_sock_write_space()

libceph: update outdated comment in ceph_sock_write_space()

The function try_write() was renamed to ceph_con_v1_try_write()
in commit 566050e17e53 ("libceph: separate msgr1 protocol
implementation") and subsequently moved to net/ceph/messenger_v1.c
in commit 2f713615ddd9 ("libceph: move msgr1 protocol implementation
to its own file").  Update the comment in ceph_sock_write_space()
accordingly.

[ idryomov: account for msgr2 in the updated comment as well ]

Signed-off-by: kexinsun <kexinsun@smail.nju.edu.cn>
Reviewed-by: Viacheslav Dubeyko <Slava.Dubeyko@ibm.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>