Update syscall.master to 4.10-rc6. Also fix comments, a typo,
and wrong numbering for a few unimplemented syscalls.

For 32-bit Linuxulator, socketcall() syscall was historically
the entry point for the sockets API. Starting in Linux 4.3, direct
syscalls are provided for the sockets API. Enable it.

The initial version of patch was provided by trasz@ and extended by me.

Submitted by: trasz
MFC after: 2 week
Differential Revision: https://reviews.freebsd.org/D9381