The ornamental design for a gamenetsupportarm, as shown and described.
FIG. 1 is a side view of a game net support arm showing the claimed design, in an environment of use;
FIG. 2 is a front perspective view of the game net support arm shown in the environment of use;
FIG. 3 is a front perspective view thereof shown without its environment;
FIG. 4 is a rear perspective view thereof;
FIG. 5 is a left-side view thereof, the right-side view being a mirror image thereof;
FIG. 6 is a front view thereof;
FIG. 7 is a back view thereof;
FIG. 8 is a top view thereof; and,
FIG. 9 is a bottom view thereof.
The broken line showing of the bases and net in FIGS. 1-2 depict environmental subject matter and form no part of the claimed design. All other broken lines depict portions of the game net support arm that form no part of the claimed design.