packet.7: Rework description of 'sockaddr_ll' fields as a list

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man7/packet.7

@@ -127,12 +127,15 @@ struct sockaddr_ll {
 .fi
 .in
 
+The fields of this structure are as follows:
+.IP * 3
 .I sll_protocol
 is the standard ethernet protocol type in network byte order as defined
 in the
 .I <linux/if_ether.h>
 include file.
 It defaults to the socket's protocol.
+.IP *
 .I sll_ifindex
 is the interface index of the interface
 (see
@@ -142,6 +145,7 @@ is the interface index of the interface
 is an ARP type as defined in the
 .I <linux/if_arp.h>
 include file.
+.IP *
 .I sll_pkttype
 contains the packet type.
 Valid types are
@@ -158,12 +162,13 @@ in promiscuous mode, and
 for a packet originating from the local host that is looped back to a packet
 socket.
 These types make sense only for receiving.
+.IP *
 .I sll_addr
 and
 .I sll_halen
 contain the physical-layer (e.g., IEEE 802.3) address and its length.
 The exact interpretation depends on the device.
-
+.PP
 When you send packets, it is enough to specify
 .IR sll_family ,
 .IR sll_addr ,