config-linux.md: Reword kernelTCP docs and mention bytes

Avoid the dangling 'using' from e9a6d94 (cgroup: Add support for
memory.kmem.tcp.limit_in_bytes, 2015-10-26, opencontainers#235).  I've tried to echo
the kernel docs by mentioning buffer memory [1].  I'd personally
prefer linking to the kernel docs and mentioning
memory.kmem.tcp.limit_in_bytes, but that seemed like too big of a
break from the existing style for this commit.

[1]: https://kernel.org/doc/Documentation/cgroup-v1/memory.txt

Signed-off-by: W. Trevor King <wking@tremily.us>

config-linux.md

@@ -259,7 +259,7 @@ The following parameters can be specified to setup the controller:
 
 * **`kernel`** *(uint64, optional)* - sets hard limit for kernel memory
 
-* **`kernelTCP`** *(uint64, optional)* - sets hard limit for kernel memory in tcp using
+* **`kernelTCP`** *(uint64, optional)* - sets hard limit in bytes for kernel TCP buffer memory
 
 * **`swappiness`** *(uint64, optional)* - sets swappiness parameter of vmscan (See sysctl's vm.swappiness)