ioctl_userfaultfd.2: Add kernel versions where each ioctl() first appeared

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man2/ioctl_userfaultfd.2

@@ -74,6 +74,7 @@ events in a consistent way.
 .\" FIXME What does "consistent" mean?
 .\"
 .SS UFFDIO_API
+(Since Linux 4.3.)
 Enable operation of the userfaultfd and perform API handshake.
 The
 .I argp
@@ -159,6 +160,7 @@ field was not zero.
 .\" zeroed out. Why is this done?
 .\"
 .SS UFFDIO_REGISTER
+(Since Linux 4.3.)
 Register a memory address range with the userfaultfd object.
 The
 .I argp
@@ -202,6 +204,9 @@ Track page faults on missing pages.
 .B UFFDIO_REGISTER_MODE_WP
 Track page faults on write-protected pages.
 .PP
+.\" FIXME Actually, the following sentence appears not to be true;
+.\" UFFDIO_REGISTER_MODE_WP seems also to be supported.
+.\" Can someone confirm?
 Currently, the only supported mode is
 .BR UFFDIO_REGISTER_MODE_MISSING .
 .PP
@@ -213,6 +218,7 @@ range in the
 field.
 .\"
 .SS UFFDIO_UNREGISTER
+(Since Linux 4.3.)
 Unregister a memory address range from userfaultfd.
 The address range to unregister is specified in the
 .IR uffdio_range
@@ -243,6 +249,7 @@ There as an incompatible mapping in the specified address range.
 There was no mapping in the specified address range.
 .\"
 .SS UFFDIO_COPY
+(Since Linux 4.3.)
 Atomically copy a continuous memory chunk into the userfault registered
 range and optionally wake up the blocked thread.
 The source and destination addresses and the number of bytes to copy are
@@ -305,6 +312,7 @@ it is not read by the
 operation.
 .\"
 .SS UFFDIO_ZERO
+(Since Linux 4.3.)
 Zero out a part of memory range registered with userfaultfd.
 The requested range is specified by the
 .I range
@@ -342,6 +350,7 @@ or an error in the same manner as
 .IR uffdio_copy.copy .
 .\"
 .SS UFFDIO_WAKE
+(Since Linux 4.3.)
 Wake up the thread waiting for page-fault resolution.
 The
 .I argp