Upgrade socat to 1.7.3.0.

The cross-compiling patch is no longer necessary.  Also added librt as a
dependency, since it is required.  This also fixes an issue where
support for linux/errqueue.h was not being detected correctly and
causing a build failure with 3.18.

Signed-off-by: John Szakmeister <john@szakmeister.net>

net/socat/patches/010-fix_cross_compiling_error.patch

@@ -1,22 +0,0 @@
---- a/configure.in
-+++ b/configure.in
-@@ -41,7 +41,7 @@ AC_CHECK_PROG(AR, ar, ar, gar)
- # fail
- AC_LANG_COMPILER_REQUIRE()
- 
--if test "$CC" = "gcc"; then
-+if test "$GCC" = yes; then
-    CFLAGS="$CFLAGS -D_GNU_SOURCE -Wall -Wno-parentheses"
-    ERRONWARN="-Werror -O0"
- elif test "$CC" = "clang"; then
---- a/configure
-+++ b/configure
-@@ -3348,7 +3348,7 @@ fi
- 
- 
- 
--if test "$CC" = "gcc"; then
-+if test "$GCC" = yes; then
-    CFLAGS="$CFLAGS -D_GNU_SOURCE -Wall -Wno-parentheses"
-    ERRONWARN="-Werror -O0"
- elif test "$CC" = "clang"; then