net: netconsole: separate fragmented message handling in send_ext_msg
Following the previous change, where the non-fragmented case was moved
to its own function, this update introduces a new function called
send_msg_fragmented to specifically manage scenarios where message
fragmentation is required.
Signed-off-by: Breno Leitao <leitao@debian.org> Reviewed-by: Simon Horman <horms@kernel.org> Signed-off-by: Paolo Abeni <pabeni@redhat.com>