lxc: containter: fix build with glibc 2.36

lxc: containter: fix build with glibc 2.36

With glibc 2.36, sys/mount.h and linux/mount.h conflict:
https://sourceware.org/glibc/wiki/Release/2.36#Usage_of_.3Clinux.2Fmount.h.3E_and_.3Csys.2Fmount.h.3E

lxc_container.c imports sys/mount.h and linux/fs.h, which pulls in
linux/mount.h.

linux/fs.h isn't required here though. glibc sys/mount.h has had
MS_MOVE since 2.12 in 2010

Reviewed-by: Erik Skultety <eskultet@redhat.com>
Signed-off-by: Cole Robinson <crobinso@redhat.com>