virsh: Split cmds to manage host interface from virsh.c

Commands to manage host interface are moved from virsh.c to
virsh-interface.c, with a few helpers for interface command use.

* virsh.c: Remove interface commands and a few helpers.
           (vshCommandOptInterface, vshCommandOptInterfaceBy)
* virsh-interface.c: New file, filled with interface commands and
                     its helpers.
* cfg.mk: Skip to check config.h including for virsh-interface.c
* po/POTFILES.in: Add virsh-interface.c

cfg.mk

@@ -773,7 +773,7 @@ exclude_file_name_regexp--sc_prohibit_xmlURI = ^src/util/viruri\.c$$
 
 exclude_file_name_regexp--sc_prohibit_return_as_function = \.py$$
 
-_virsh_includes=(edit|domain-monitor|domain|volume|pool|network)
+_virsh_includes=(edit|domain-monitor|domain|volume|pool|network|interface)
 exclude_file_name_regexp--sc_require_config_h = ^(examples/|tools/virsh-$(_virsh_includes)\.c$$)
 
 exclude_file_name_regexp--sc_require_config_h_first = ^(examples/|tools/virsh-$(_virsh_includes)\.c$$)

po/POTFILES.in

@@ -180,6 +180,7 @@ tools/virsh.c
 tools/virsh-domain-monitor.c
 tools/virsh-domain.c
 tools/virsh-edit.c
+tools/virsh-interface.c
 tools/virsh-network.c
 tools/virsh-pool.c
 tools/virsh-volume.c