flow_dissector: Address kdoc warnings

Address a number of warnings flagged by
./scripts/kernel-doc -none include/net/flow_dissector.h

 include/net/flow_dissector.h:23: warning: Function parameter or member 'addr_type' not described in 'flow_dissector_key_control'
 include/net/flow_dissector.h:23: warning: Function parameter or member 'flags' not described in 'flow_dissector_key_control'
 include/net/flow_dissector.h:46: warning: Function parameter or member 'padding' not described in 'flow_dissector_key_basic'
 include/net/flow_dissector.h:145: warning: Function parameter or member 'tipckey' not described in 'flow_dissector_key_addrs'
 include/net/flow_dissector.h:157: warning: cannot understand function prototype: 'struct flow_dissector_key_arp '
 include/net/flow_dissector.h:171: warning: cannot understand function prototype: 'struct flow_dissector_key_ports '
 include/net/flow_dissector.h:203: warning: cannot understand function prototype: 'struct flow_dissector_key_icmp '

Also improve indentation on adjacent lines to those changed
to address the above.

No functional changes intended.

Signed-off-by: Simon Horman <horms@kernel.org>
Link: https://lore.kernel.org/r/20230419-flow-dissector-kdoc-v1-1-1aa0cca1118b@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>