This change adds support for semi-standard IPPROTO_ICMP AF_INET datagram sockets. This replaces the old ad hoc, nonstandard way of implementing ping with a more standard, socket interface.

Squashed commit of the following:

    net/icmp:  Finishes off icmp_recvfrom().
    net/icmp:  Add readahead support for IPPROTO_ICMP sockets.
    net/icmp:  Add poll() support for IPPROTO_ICMP sockets.
    net/icmp:  Add a connection structure for IPPROTO_ICMP sockets.
    net/icmp:  Implements sendto for the IPPROTO_ICMP socket.
    net/icmp:  Move icmp_sendto() and icmp_recvfrom() to separate files.  They are likely to be complex (when they are implemented).
    net/icmp:  Hook IPPROTO_ICMP sockets into network.  Fix some naming collisions.  Still missing basic ICMP send/receive logic.
    configs: apps/system/ping current need poll() enabled.
    configs: All defconfig files that use to enable low-level support must now enabled CONFIG_SYSTEM_PING.
    net/icmp:  Adds basic build framework to support IPPROTO_ICMP sockets.

configs/lm3s6432-s2e/nsh/defconfig

@@ -10,12 +10,11 @@ CONFIG_ARCH_STACKDUMP=y
 CONFIG_ARCH="arm"
 CONFIG_ARMV7M_TOOLCHAIN_CODESOURCERYL=y
 CONFIG_BOARD_LOOPSPERMSEC=4531
-CONFIG_DISABLE_POLL=y
 CONFIG_EXAMPLES_NSH=y
 CONFIG_MAX_TASKS=16
 CONFIG_MAX_WDOGPARMS=2
 CONFIG_NET_BROADCAST=y
-CONFIG_NET_ICMP_PING=y
+CONFIG_NET_ICMP_SOCKET=y
 CONFIG_NET_ICMP=y
 CONFIG_NET_MAX_LISTENPORTS=8
 CONFIG_NET_SOCKOPTS=y
@@ -48,6 +47,7 @@ CONFIG_SDCLONE_DISABLE=y
 CONFIG_START_DAY=8
 CONFIG_START_MONTH=5
 CONFIG_START_YEAR=2010
+CONFIG_SYSTEM_PING=y
 CONFIG_TASK_NAME_SIZE=0
 CONFIG_TIVA_BOARDMAC=y
 CONFIG_TIVA_ETHERNET=y