tc-mpls: fix manpage example and help message string

tc-mpls: fix manpage example and help message string

Manpage:
 * Remove the extra "and to ip packets" part from command description
   to make it more understandable.

 * Redirect packets to eth1, instead of eth0, as told in the
   description.

Help string:
 * "mpls pop" can be followed by a CONTROL keyword.

 * "mpls modify" can also set the MPLS_BOS field.

Signed-off-by: Guillaume Nault <gnault@redhat.com>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>